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PHYSICAL GEOGRAPHY 



WILLIAM MOEEIS DAVIS 

■PROFESSOK OF PHYSICAL GEOGKAPHY IN HAKVABD UNIVERSITY 



ASSISTED BY 



WILLIAM HENRY SNYDER 

MASTEK Ijr SCIENCE IN WORCESTER ACADEMY 



Boston, U.S.A., and London 
GINN & COMPANY, PUBLISHERS 

1898 

L. 



A OSS 

■J) ^7 



21889 

Entered at Stationers' Hall 



Copyright, 1898, by 
WILLIAM MOKRIS DAVIS 



ALL RIGHTS RESERVED 




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PREFACE. 



The successful development of Geography, considered 
as the study of the earth in relation to man, must be 
founded on Physical Geography, — or Physiography, as 
it is coming to be called, — the study of man's physical 
environment. No rational or scientific advance can be 
made in the former without an appropriate preparation 
in the latter. The earth's physical features must not 
only be described, — they must be explained, so that the 
understanding shall aid the memory in holding them in 
mind. They must not be presented apart from the man- 
ner in which they affect man's ways of living ; attention 
must frequently be drawn to the association of human 
conditions with the environment by which they have been 
determined, in order to form the habit of looking at the 
features of the earth as prime factors in guiding the 
development of mankind. In brief, physiographic facts 
should be traced back to their causes and forward to their 
consequences ; and thus the phrase " causes and conse- 
quences " comes to serve as a touchstone by which the 
treatment of the subject may be tested. 

It does not, however, seem advisable to make this test 
absolute in an elementary book, for the causes 'of certain 
important facts may be complicated, as is the case with 
the atmospheric circulation ; or unknown, as in the con- 



•^ PREFACE. 



fio-uration of the continents and in the uplift and depres- 
sion of the lands; and the consequences of other facts 
may be indirect or remote, as with the temperature of 
the deep sea and the configuration of the sea bottoms. 
Yet in all these cases the facts are so inherently physio- 
graphic that they should not be omitted. Nevertheless 
the test of " causes and consequences " has been, as far 
as practicable, applied in the preparation of this book. 

The subject of Physical Geography, or Physiography, 
may be naturally divided into four parts : the earth as a 
globe, the atmosphere, the oceans, and the lands. Extra- 
neous subjects, however interesting or important in them- 
selves, such as the non-geographical elements of astronomy, 
the principles of physics, and the divisions of geological 
time, are carefully excluded. When so much space is 
demanded for the due consideration of strictly physio- 
graphic matter, none can be afforded for irrelevant topics. 
An examination of the book under such index headings 
as agriculture, animals, forests, plants, etc., will show that 
the organic environment of man, a large subject in itself, 
is by no means neglected. It is touched upon because 
it affords many excellent illustrations of the manner in 
which the earth's physical features determine the distri- 
bution of plants and animals, as well as of man ; but the 
actual distribution of plants and animals, like that of 
land forms or of nations, is not considered. 

Regarding the earth as a globe, it is hoped that the 
observational exercises suggested in the Appendix may 
be undertaken even before geometry is studied; for in 
no other way can so clear an understanding of such topics 
as the form, size, and rotation of the earth, with their 



PBEFACE. V 

applications in latitude and longitude, be obtained. Ob- 
servational work of this kind may be mucli strengthened 
if it is led up to by simple observations of the stars 
in earlier years. Attention may be directed to the para- 
graphs on the origin of the earth's shape, and the conse- 
quences of its shape, size, and rotation, as illustrations of 
the method of treatment above referred to. 

The thorough study of the atmosphere demands a 
knowledge of physics such as cannot be assumed on 
the part of those for whom this book is intended. For 
this reason the chapter on the atmosphere is made brief 
and elementary. It should be supplemented by local 
observations and by the construction and study of weather 
maps, as suggested in Appendixes H and I. The atmos- 
phere is of geographical importance chiefly through weather 
and climate, and these subjects are repeatedly touched 
upon in later chapters. 

The study of the ocean affords less opportunity for 
observation than the other divisions of the subject, but 
its relation to climate is of great importance, the mono- 
tony of the sea bottom may be effectively presented in 
contrast with the variety of the lands, and the topics of 
waves and tides are of much disciplinary value. 

The lands have come to be the seat of the highest forms 
of plant and animal life, as well as the home of man, 
because of the variety of physical conditions that they 
afford. It is therefore fitting that the largest part of a 
book on Physical Geography should be devoted to this 
part of the subject. Moreover, great progress has been 
made in explaining the forms of the land during the 
last half of the nineteenth century, and thus it has now 



VI PREFACE. 

become possible to classify and describe land forms with 
something of scientific accuracy. But as this method of 
treatment is to a certain extent novel, it is entered upon 
with careful choice of simple forms, such as coastal plains, 
which are susceptible of elementary treatment, and the 
first examples are presented deliberately. The meaning 
of the various details of form is thus made so manifest 
as to establish the expectation that all land forms may, 
in due order, be rationally explained. At the same time 
the products characteristic of various land forms, together 
with the control that they exert over the location of settle- 
ments and the distribution of industries, are directly asso- 
ciated with the forms themselves, in order to emphasize 
their human relations. In addition to the ideal type 
forms that are frequently introduced, abundant reference 
is made to actual examples of the types, and practical 
value is thus given to a treatment that would otherwise 
be too theoretical. Nearly every place thus mentioned 
can be located by means of the small regional maps in 
the text, or upon the maps at the end of the book; the 
subject is thus made definite and specific. 

Technical terms are avoided in nearly all cases. Geo- 
logical processes, such as deformation and denudation, are 
presented in as simple a manner as possible ; emphasis is 
always given to the physiographic forms resulting from 
the processes, and not to the processes themselves. The 
insertion of a chapter on rivers and valleys in the latter 
part of the book does not mean that these important 
topics have not been encountered earlier ; they have been 
mentioned wherever needed in connection with the pre- 
ceding chapters, but certain features especially associated 



PREFACE. vii 

with rivers are best taken up independently after the more 
important land forms have been described, and to these 
Chapter IX is devoted. 

The study of the text on land forms should be supple- 
mented as far as possible by appropriate observations in 
the field. Nearly all schools can make occasional excur- 
sions in which some of the activities of the lands (p. 99) 
and some examples of typical land and water forms may 
be examined. It is especially desirable that, at such times, 
comparisons should be made between the locality visited 
and its representation on the best available large scale 
map, in order that some real appreciation of the art of 
map reading may be acquired. After such a beginning 
the maps referred to in Appendix M will have a greatly 
increased value as illustrations of typical land forms not 
accessible in the home district. For the same reason 
written descriptions of localities visited should be pre- 
pared by teacher and students ; thus the descriptions of 
remote localities referred to in Appendix L will gain 
increased reality. Photographs of scenes familiar on 
home excursions will give a new value to photographs of 
distant scenes, especially if both are exhibited by lantern 
projection. 

The opening paragraphs of each chapter are intended 
to serve as reading lessons rather than as texts for study 
and recitation. An outline of the subject may be pre- 
sented in a brief course by omitting more or less of the 
smaller-type text. The chapters on the Waste of the 
Lands and the Chmatic Control of Land Forms may be 
omitted in a short course. The topics discussed in the 
Appendixes may be entirely disregarded if they seem too 



viii PEE FACE. 

difficult for the pupils who are using the book ; they will, 
on the other hand, be found useful extensions of the text 
for more advanced classes. 

The author has had the advantage of association with 
Mr. W. H. Snyder, master in Science in Worcester (Mass.) 
Academy, whose experience in teaching has been of much 
assistance in adapting the text to the needs of secondary 
schools. The proof-sheets have been examined by Mr. 
M. Grant Daniell, late principal of Chauncy-Hall School, 
Boston, Mr. W. C. Moore, instructor in Science in the 
Salem (Mass.) Normal School, and Mr. H. C. Wood, in- 
structor in Physical Geography in the Cleveland (Ohio) 
High School, to whom the thanks of the author are due 
for many valuable suggestions. 

Cambridge, Mass., 
September, 1898. 



CONTENTS, 



CHAPTER PAGE 

I. Introduction ......... 1 

11. The Earth as a Globe ...... 8 

III. The Atmosphere ........ 18 

IV. The Ocean 57 

V. The Lands 91 

VI. Plains and Plateaus . . ". , . . . 113 

VII. Mountains 159 

VIII. Volcanoes 199 

IX. Rivers and Valleys . . . . . . . 222 

X. The Waste of the Land 263 

XL' Climatic Control of Land Forms 297 

XII. Shore Lines 347 

Appendixes ......... 385 

Index 419 

Reference Maps ........ 430 



LIST OF ILLUSTRATIONS. 



FIG. PAGE 

1. Dwarfs in the Equatorial Forest 3 

2. Eskimo hunting Walrus 5 

3. Eclipse of the Moon, showing the Curved Edge of the Earth's 

Shadow 11 

4. Height of Land and Depth of Sea compai'ed to Curvature of 

Earth's Surface 14 

5. Meridians and Parallels 17 

6. Bedouins of the Sahara 18 

7. Barometer 23 

8. Grizzly Bears suffocated in Death Gulch, Yellowstone Park . . 26 

9. Direct and Oblique Bays 26 

10. The Comey Self-Recording Thermometer 27 

11. Chart of Mean Annual Temperatures 28 

12. Illustration of an Isothermal Line 29 

13. The Planetary Circulation of the Atmosphere 30 

14. Wet- Weather Streams of the Tarso Mountains, Sahara ... 31 

15. Spiral Wind Courses 33 

16. Isotherms for January 34 

17. Isotherms for July 35 

18. Diagrams of Terrestrial Winds for January and July .... 37 

19. Winds of January 38 

20. Winds of July . 39 

21. Winds of the Atlantic Ocean in January and July 40 

22. Chart of Equal Annual Range of Temperature 42 

23. Monsoons of Northern Summer 43 

24. Monsoons of Southern Summer 43 

25. Chart of Annual Rainfall 46 

26. Weather Map (first day) 50 

27. Weather Map (second day) 50 

28. Weather Map (third day) 51 

29. Weather Map (fourth day) 51 

30. An Ocean Steamship 57 



xii LIST OF ILLUSTRATIONS. 

FIG. PAGE 

31. Land and Water Hemispheres 60 

32. Sounding Instrument and Water Bottle 61 

■ 33. Deep-Sea Thermometers . . 61 

34. Dredge ......'..' 62 

35. Curves of Ocean Temperaturej i . . ' . ...."'... 64 

36. A Vessel beset hy Pack Ice 65 

37. An Iceberg 66. 

38. Globigerina .................. 68 

39. Temperatures of the Caribbean Sea 69 

40. Section of Continental Shelf 70 

41. Orbital Movement of Water in Waves 72 

42. Surf 75 

43. Chart of Ocean Currents 77 

44. Displacement of a Vessel by Currents 78 

45. Drift of Floating Objects by Currents 78 

46. Currents of the Indian Ocean in July 80 

47. Currents of the Indian Ocean in January 80 

48. Temperatures on the Atlantic 82 

49. High Tide 83 

50. Low Tide 84 

51. Diagram showing Progression of High Tide up a Bay . ... 85 

52. Diagram of Tide Waves 85 

53. The Tidal Wave, or Bore, in the Seine 87 

54. A Floating Jellyfish 88 

55. Deep-Sea Fish 89 

56. Deep-Sea Crustacean '.X- -i ^ • t '• •■ • 89 

57. Deep-Sea Sponge .•:...... 90 

58. Height of Land and Depth of the Sea 94 

59. A Quarry showing Weathered Rock 100 

60. Granite 101 

61. Pebbly Sandstone 102 

62. Limestone with Fossil Shells 102 

63. Beavers 107 

64. Caribou 108 

65. Jaguar 108 

66. Tiger 109 

67. Cassowary 109 

68. Kangaroo 110 

69. Southern New Jersey 113 



LIST OF ILLUSTRATIONS. xiii 

FIG. PAGE 

70. The Beach, Atlantic City, New Jersey 115 

71. Mountains bordering the Sea . . . . .• . . . ." . . 117 

72. Narrow Coastal Plain 119 

73. Coastal Plain of Mexico 121 

74. Coastal Plain of India 122 

75. Broad Coastal Plain 123 

76. Coastal Plain of the Carolinas ........ . . . 124 

77. North Carolina Truck Farm . 126 

78. Artesian Well 127 

79. Diagram of. the Fall-Line . 128 

80. Embayed Coastal Plain 129 

81. A Branch of Chesapeake Bay, Maryland 131 

82. A Belted Coastal Plain 132 

83. The Coastal Plain of Alabama 134 

84. Pine Forest on Coastal Plain, Alabama 135 

85. Ancient Coastal Plain of Wisconsin 136 

86. Ancient Coastal Plain of Ontario and New York 138 

87. Diagram of Ancient Coastal Plain of Middle England . . . 139 

88. A Plateau in Arizona 141 

89. Diagram of Narrow Canyon ............ 142 

90. Diagram of Widened Canyon 143 

91. Diagram of a Waterfall in a Canyon 144 

92. The Allegheny Plateau 147 

93. Canyon of Kanawha River in Allegheny Plateau, West Virginia 148 

94. The Enchanted Mesa, New Mexico 151 

95. The Ozark Plateau, Missouri 154 

96. Section of the Ozark Plateau 154 

97. Broken Plateaus 155 

98. Diagram of Blocked Plateaus 156 

99. Hurricane Ledge 157 

100. The Himalaya Mountains 159 

101. Block Mountains 161 

102. Mountains of Southern Oregon 162 

103. A Dissected Mountain Range, Utah 165 

104. Fractured Slopes of Rock Waste at Base of Mountain Range, 

Nevada 166 

105. Diagram of the Jura 168 

106. Diagram of the Black Hills 170 

107. Deadwood, a Mining Town in the Black Hills 171 



xiv LIST OF ILLUSTRATIONS. 

FIG. PAGE 

108. Peaks of the Central Alps 172 

109. An Alpine Ridge of Slanting Layers 173 

110. An Avalanche Path, Selkirk Range, Canada 178 

111. Path of an Ice Tall in the Alps 179 

112. A Mountain of Down-Folded Layers 180 

113. A Landslide in the Himalaya 182 

114. Ibex 186 

115. The Mountains of North Carolina 187 

116. The Piedmont Belt, Virginia 189 

117. Map of the Piedmont Belt, Virginia ....:.... 189 

118. Diagram of the Allegheny Mountains, Pennsylvania . . . 190 

119. Gorge of the Rhine in the Slate Mountains, Germany . . . 191 

120. The Upland of New England, with Monadnock in the Distance 192 

121. Valley of the Deerfield in the New England Upland .... 193 

122. Model of Embayed Mountains 195 

123. Diagram of Baraboo Ridge, Wisconsin 197 

124. Vesuvius in Eruption 200 

125. Monte Nuovo 202 

126. The Cinder Cone and Lava Flow, California 204 

127. Excavations in Herculaneum 206 

128. A Volcanic Island (section and plan) 209 

129. Lava Flows on the Plateaus of Arizona 210 

130. The Lava Plateau of Idaho, Oregon, and Washington . . . 211 

131. Diagram of a Caldera 212 

132. Deception Island, a Volcanic Caldera (plan and section) . . 213 

133. The Cone of Vesuvius in the Caldera of Monte Somma . . 213 

134. Contour Map of Mount Shasta, California 214 

135. Mount Shasta . 215 

136. Mount Hood 215 

137. Contour Map of Crater Lake, Oregon 216 

138. Mount Johnson, near Montreal, Canada 217 

139. Volcanic Necks, Arizona 217 

140. Dissected Lava Plateau of Southern India 218 

141. Diagram of a Young Volcano in the Background, changed by 

Erosion to Lava-Capped Mesas in the Foreground . . . 220 

142. Diagram of Dike and Mesa 221 

143. Mohawk Valley ■ 223 

144. Diagram of Cavern and Sink Hole 225 

145. Natural Bridge, Syria 226 



LIST OF ILLUSTRATIONS. XV 

FIG. PAGE 

146. Diagram showing Distribution of Ground Water 227 

147. A Geyser 229 

148. Niagara Falls 231 

149. Falls of the Yellowstone River 2-35 

150. Diagram of Torrent with Falls and Reaches 236 

151. Diagram of a Straight Valley 240 

152. Diagram of a Crooked River widening its Valley .... 241 

153. Contour Map of the Missouri River Valley 242 

154. A Meandering River on the Plain of Hungary 244 

155. Meanders of the Mississippi 245 

156 a, b, c. Diagrams of a Shifting Divide 247 

157. Diagram of Shifting River Divides 248 

158. Diagram of Rearranged River Courses 248 

159. Boundary of Georgia and South Carolina 249 

160. Outline Map of Eastern France and Western Germany . . 249 

161. Irregular Course of the Meuse in its Meandering Valley . . 250 

162. Diagram Of a Narrowed Spur 253 

163. Diagram of a Cut-Off Spur 254 

164. Entrenched Meanders of the Neckar 254 

165. Entrenched Meanders of the Moselle 255 

166. Transverse and Longitudinal Streams 256 

167. Transverse and Longitudinal Valleys 256 

168. Watergap of the Susquehanna in North Mountain, Pennsylvania 257 

169. Contour Map of the Susquehanna Watergap in North Momi- 

tain, Pennsylvania . .' 257 

170. Map of Narragansett Bay 260 

171. The Hudson River, looking North from West Point . . . 261 

172. Rock Waste on Mountain Slopes 264 

173. A Lake-Floor Plain <' 265 

174. Cliff and Talus 269 

175. Land Slides in the San Juan Mountains, Colorado .... 270 

176. The Slope of Pikes Peak 272 

177. Alluvial Fans 276 

178. An Eroded Valley 278 

179. A Filled Valley 279 

180. Flood Plain of Red River, Louisiana 280 

181. A Terraced Valley 281 

182. A Lake-Floor Plain . 281 

183. A Warped Valley 282 



xvi LIST OF ILLUSTRATIONS. 

FIG. PAGE 

184. A Waste-Filled Basin, Southern California 282 

185. A Plain of Mountain Waste, Southeastern California . . . 283 

186. A Meandering River, Vale of Kashmir 284 

187. The Green River Basin, Wyoming 285 

188. The Mississippi Flood Plain 287 

189. View of River-Made Plain of Northern India 290 

190. The Valley of California 291 

191. The Delta of the Mississippi 293 

192. Torrent Fan, Lake Geneva 295 

193. Flood in Cherry Creek, Denver, Colorado . . , 300 

194. Diagram of the Colorado River Delta 302 

195. A River Valley in Desert Mountains, Peru 302 

196. Bad Lands 303 

197. The Waste-Filled Floor of Death Valley, Southeastern California 308 

198. Half-Buried Mountain Range, Nevada 309 

199. Home of the Farmer Ant 310 

200. Diagram of Outward Drainage of Interior Basin, Himalaya . 312 

201. Diagram of a Waste-Filled Trough . 313 

202. Sand Dunes in Sahara 315 

203. Buffalo 316 

204. Loess Beds, Yellovv^ River Basin, China 317 

205. Lakes Bonneville and Lahontan 319 

206. The Yucca .320 

207. Camel 321 

208. El Kantara Oasis, Algerian Sahara 323 

209. Rosegg Glacier in the Alps 327 

210. Viesch Glacier in the Alps 328 

211. Glacial Moraines, Sierra Nevada, California 331 

212. Glaciated Area of the Northern United States 332 

213. Diagram of an Ice Sheet 333 

214. Diagram of a Retreating Ice Sheet 333 

215. Glacial Moraines, North Dakota 335 

216. An Esker 336 

217. A Glacial Boulder 337 

218. A Drumlin 338 

219. The Glacial Lake Agassiz 340 

220. Lake in the Adirondacks, New York 342 

221. Ice- Worn Rocks, Coast of Maine . 344 

222. Sea Cliffs, Grand Manan, New Brunswick ....... 348 . 



LIST OF ILLUSTRATIONS. xvii 

PIG. PAGE 

223. Diagrams of Coastal Plain Shore Lines 351 

224. The Hooked Spit of Cape Lookout 352 

225. A Tidal Inlet and Delta 353 

226. The Sea Cliffs of Normandy 355 

227. Valleys in the Cliffed Uplands of Normandy 356 

228. Diagram of an L'regular Shore Line 358 

229. A Delta in a Norwegian Fiord 359 

230. The " Old Man of Hoy " 361 

231. Cliffs and Deltas on an Irregular Shore Line 362 

2.32. A Curved Shore Line 363 

233. Diagram of a Eetreating Shore Line 364 

234. Gibraltar 366 

235. Easdale 367 

236. Headlands and Bays 368 

237. The Coast Platform of Norway 369 

238. Deltas of the Texas Coast 371 

239. Mangrove Tree 373 

240. A Fringing Reef 374 

241. A Barrier Reef 375 

242. Part of the Great Barrier Reef of Australia . . . . . . 376 

243. Diagram of Part of a Barrier Reef 377 

244. Diagram of Part of an Elevated Reef 377 

245. Diagram of Part of a Denuded Reef enclosed by a Barrier Reef 378 

246. Diagram of Part of a Drowned Reef 378 

247. A Large Atoll 379 

248. An Atoll or Coral Island 380 

249. Metia, an Elevated Coral Island 382 

250. A Small Atoll 383 

251. Globular Form of Earth shown by Visibility of Stars . . . 385 

-" 252. Sun Altitudes on the Two Slopes of a Hill 386 

--''^53. Sun Altitudes measured in a School Yard 386 

254. Sun-Circle Method of Measuring Latitude 390 

255. Latitude on a Spheroidal Earth 391 

256. The Stereographic Projection 394 

257. The Mercator Projection ,. 395 

258. The Conical Projection 395 

259. Representation of Relief by Hachures 396 

260. Lines of Equal Magnetic Variation 399 

261. The Tidal Problem 406 



ACKNOWLEDGMENTS OF ILLUSTRATIONS. 

The following acknowledgments are due for the illustrations used in 
this book. The sources of a very few cannot at present be determined 
and are not acknowledged. 

Adams, Prof. F. D., Fig. 138. 

Caroline Island Eclipse Expedition, Fig. 248. 

Dana, Coral Islands, Fig. 249. 

Davis, Elementary Meteorology, Figs. 11, 16, 17, and 22. 

Frye, Complete Geography, Figs. 30, 36, 53, 63, 64, 65, 66, 68, 84, 114, 
115, 121, 136, 174, 189, 203, 204, 207, 209, 210, 222. 

Gardner Collection of Photographs, Harvard University, Figs. 37, 42, 
49, 50, 59, 100, 107, 108, 109, 113, 116, 120, 124, 127, 135, 143, 145, 147, 
148, 149, 168, 171, 172, 176, 195, 197, 208, 218, 220, 229, and 242. 

Giekie, Scenery of Scotland, Fig. 2-30. 

Harvard College Astronomical Observatory, Fig. 3. 

Harvard College Botanical Department, Fig. 206. 

Harvard Geographical Models, Figs. 71, 72, and 122. 

Heine, Prof., Fig. 111. 

Knott, L. E., Apparatus Co., Figs. 7 and 10. 

Lummis, Fig. 94. 

Maryland Geological Survey, Fig. 81. 

Mayer, A. G., Fig. 239. 

Mississippi River Commission, Fig. 155. 

Nansen, Eskimo Life, Fig. 2. 

North Carolina Geological Survey, Fig. 77. 

Eeport of the Challenger Expedition, Fig. 38. 

Richards, Prof., Fig. 193. 

Schirmer, Le Sahara, Fig. 6. 

Schmidt's Atlas of Vesuvius, Figs. 125 and 133. 

Stieler's Hand Atlas, Figs. 14 and 234. 

Thomson, Voyage of Challenger, Fig. 34. 

Three Cruises of the Blake, Figs. 55, 56, and 57. 

Topographical Map of the German Empire, Figs. 164 and 165. 

Topographical Map of France, Fig. 161. 

U. S. Coast Survey, Figs. 191, 224, and 225. 

U. S. Geological Survey, Figs. 8, 88, 93, 95, 99, 104, 126, 129, 134, 137, 
139, 153, 169, 175, 196, 205, 211, 212, and 215. 

Woodworth, W. McM., Fig. 54. 



PHYSICAL GEOGRAPHY. 

c«3j@<oo 

CHAPTER I. 
INTRODUCTION. 

The Relation of Man to the Earth. 

Physical Geography treats of the many kinds of sur- 
roundings that man finds in different parts of the world. 
It describes the various features of the earth that influence 
the manner in which man lives upon it. Hence it must 
consider the form of the earth as a whole, the climates of 
its different parts, the movements of its ocean waters, and 
the forms of its lands ; it must give some account of the 
rocks and soils that are characteristic of different kinds of 
land forms, and it must explain the physical agencies that 
control the distribution of plants and animals. When 
the more important elements of this great subject are 
learned, a good understanding may be gained of the way 
in which climate, land forms, and other features of the 
earth exercise a control over the habits and customs of 
mankind. 

For example, high temperatures must prevail around 
the equator of a globe rotating and warmed like the earth 
by the rays of a hot sun. The warm and moist air of the 
equatorial belt will frequently be cloudy, and rain will 



2 . PHYSICAL GEOGRAPHY. 

be plentiful. Vegetation will thrive in a region always 
warm and moist; animal life will be abundant; but the 
heat and dampness of the climate, the heavy forest growth, 
and the abundance of animal life make such a region 
unfavorable to the higher development of man. No people 
native to the equatorial forests have ever advanced by 
their own unaided efforts far towards the conditions of 
civilization. 

On the other hand, it will be found that on a globe 
rotating like the earth a low temperature must prevail in 
the polar regions where sunshine is weak, and snow will 
be more common there than rain. As the snow gathers 
on the polar lands and its under part is compacted into 
ice, much of the surface will be frozen and barren. Plants 
cannot flourish in so wintry a region, and land animals 
cannot be numerous. It is easy to understand that the 
people inhabiting polar lands must be surrounded by 
unfavorable conditions, so that they cannot rise above a 
low condition of life. 

The following paragraphs present special illustrations 
of these principles. 

The Dwarfs of the African Forests. — The equatorial 
belt of Africa is in large part a densely forested wilderness. 
Tall trees spread their branches aloft, shading the ground 
all the year with their heavy foliage. Vines and creepers 
climb the trees and hang from bough to bough in great 
festoons, and the shady and damp ground is covered by a 
thick undergrowth of bushes with stems and branches so 
closely interlaced that it is almost impossible to make 
one's way through them without cutting a passage. Even 



INTRODUCTION. 



the wild animals of the forest go and come by paths that 
they keep open by frequent passing. Objects near at 
hand are hidden from sight ; the explorer cannot tell 
what is ahead of him in the gloom of the forest until he 
is close upon it. Vegetation is here so luxuriant that it 
is a burden upon the people who live amid its abundant 
growth. 

Some of the savages of this great forest are Dwarfs, 
from three to four and a half feet in height. They do 




Fig. 1. — Dwarfs in the Equatorial Forest. 



not try to make clearings and to cultivate fields, but 
search out the more open parts of the forest and build 
their villages where the undergrowth is least dense. They 



4 PHYSICAL GEOGRAPHY. 

have some trade with other tribes, but live chiefly by 
hunting wild game, which is generally plentiful and of 
great variety. Although entirely ignorant of many simple 
arts practised by the people of more open countries, the 
Dwarfs are expert in all the ways of forest life. They 
can travel quickly through the woods, knowing all the 
paths and open places. They protect their villages from 
the attacks of neighboring tribes by planting sharpened 
stakes in the paths that lead to them. They dig pitfalls 
in the narrow forest paths, covering them with sticks and 
leaves, and in this way capture even the larger wild ani- 
mals. They prepare a poison from certain plants, and tip 
their spears and arrows with it ; and in spite of their 
small size, they are formidable enemies. 

The Eskimos of Greenland. — How strikingly different 
are the conditions of life in the cold, desolate regions of 
Greenland ! Most of the land there is covered, all the 
year round with ice and snow — a vast cold desert. A 
narrow belt along the coast is free from snow in summer, 
and here live a few tribes of Eskimos ; but the ground is 
so barren that they get little support from it. The only 
tree-like plants are of stunted growth, seldom over two or 
three feet high. The herbage consists chiefly of mosses 
and lichens, which grow for a time in summer when the 
frozen ground is thawed for a few inches below the sur- 
face. A small supply of wood comes from the trunks of 
trees that are occasionally drifted by ocean currents from 
warmer regions to Arctic shores ; but there is so little of 
it that many articles which might be made of wood else- 
where are here made from the bones of sea animals. 



INTRODUCTION. 




Fig. 2. — Eskimo hnnting WalrDS. 



The Eskimos travel in sleds drawn by dogs over the 
snow-covered land or the frozen sea. They make slender 
canoes, called kayaks, which they paddle very skilfully 
when hunting seals and 
walruses. Until visited 
by Europeans and Ameri- 
cans, the Eskimos were 
as ignorant of the rest of 
the world as were the 
African Dwarfs; yet so 
well have they learned to 
take every advantage of 
their frigid surroundings that they survive where men 
from a more civilized nation, unused to living in so bar- 
ren a region, might perish. 

The Relation of Man to his Surroundings. — These brief 
accounts of the Dwarfs and the Eskimos show very 
clearly that, as a rule, the local features of the regions 
in which they live exercise a strong control over their 
manner of living. The Eskimos know nothing of forests, 
pitfalls, and poisoned arrows. The Dwarfs know nothing 
of snow and ice, sleds, kayaks, and harpoons. But each 
of these groups of people has become well practised in 
certain habits and customs that enable them to secure 
food, shelter, and reasonable safety of life ; and these 
habits and customs are closely related to the surroundings 
in which they have been acquired. 

The further the world is examined, the more general 
this rule is found to be. Whether we read about the 
wandering herdsman on the plains of western Siberia, or 



6 PHYSICAL GEOGRAPHY. 

about the fisherman who sails to the banks of Newfound- 
land, man is everywhere found making an effort to gain the 
best advantage from his surroundings. In one region he 
may be a savage, living in the rudest manner, ignorant of 
all but the simplest arts ; each individual working in about 
the same way as any other in the search for food and 
shelter. Here the relation of man's habits to his sur- 
roundings is easily understood. In another region he may 
be one of a civilized nation, where great progress has been 
made in the arts and sciences, and where each individual 
gains his livelihood not by working independently, but by 
doing -something that will serve the needs of many other 
persons besides himself. Here the relation between man's 
way of living and his surroundings may be very compli- 
cated, but it may always be discovered by careful study. 

Causes and Consequences. — It is the plan of this book 
on Physical Geography to explain the cause or origin of 
the more important kinds of physical features of the earth, 
and to trace them to their consequences as seen in the 
conditions of mankind. For example, deep valleys among 
high mountains will be found to have their origin in the 
long-continued action of weather and streams; The people 
who live in such valleys are, in consequence of the enclo- 
sure by lofty ridges, comparatively secluded from the rest 
of the world ; hence they generally preserve old-fashioned 
ways of living, which the peoj)le of a more open country 
have given up for newer ways. Bays are in most cases 
to be explained as drowned valleys ; that is, they result 
from a slow sinking of the land, by which the waters of 
the ocean are allowed to advance on the continental 



INTRODUCTION. 7 

borders; the advance is further along the valleys than 
elsewhere, and thus bays are formed on the coast line. 
The quiet water of bay heads offers protected harborage 
to shipping ; hence populous commercial cities are often 
found bordering bay heads. The fine and deep soil of 
many prairies is the sediment deposited on the bottom of 
ancient lakes whose waters were long ago drained away ; 
the soil of other prairies has been formed in an even more 
peculiar manner. Pasturage and food plants thrive in fine 
soil if the climate is favorable; hence the prairies of the 
Mississippi valley, in the mid-temperate zone, have come 
to be occupied by a great agricultural population. 

There are numerous features of the world whose causes 
and consequences are as striking and as important as those 
just mentioned. Many of them will become familiar to 
the student of this book. Many others will be found 
if the student, when travelling over the world in later 
years, seeks to understand the relation of man to the 
earth. 



CHAPTER II. 
THE EARTH AS A GLOBE. 

The Relation of the Earth to Other Bodies. 

Relation of the Earth to the Sun Few of the dis- 
coveries ever made by man have been more ojoposed to 
his early beliefs than that the earth turns on its axis once 
a day, and that it moves around the sun once a year ; for 
nothing is more natural than to suppose that the firm earth 
stands still in the center of the universe, and that all the 
bodies of the sky turn around it. What is more difficult 
than really to conceive that we turn "upside down" every 
day without knowing it, and that we are always rushing 
along, 18.5 miles a second, or over one and a half million 
miles a day, on our great annual journey of over 600,000,- 
000 miles around the sun? 

The sun, glowing with extreme heat, has the enormous 
diameter of 866,500 miles. If the earth were placed at 
the sun's center, and the moon were moving around the 
earth at its present distance of 240,000 miles, the sun 
would still reach almost 200,000 miles beyond the moon 
on all sides. Even at the great distance of 93,000,000 
miles, the sun gives abundant heat and light to the earth. 
So huge a body is a fitting center for the earth to move 
around. 

The stars are distant suns, so exceedingly remote that a 
ray of light, which travels from tlie sun to the earth in 



THE EARTH AS A GLOBE. 9 

eight minutes, would be about three and a half years on 
the journey to us from the nearest star. Many of the 
stars are believed to be larger than the sun. 

Relation of the Earth to Other Planets. — There are a 
number of other bodies which, like the earth, move around 
the sun. To the naked eye they look like stars, brighter 
or fainter, according to their size and their distance from 
the sun ; the telescope shows them to be of globular form. 
Some of them are smaller, some larger than the earth. 
Some of them turn on their axes more rapidly than the 
earth, some much less rapidly. Some of them are nearer 
to the sun than the earth is and some of them are further 
away. Some of them move around the sun in a shorter 
period and some in a longer period than that of the earth's 
journey. These bodies are called planets. The brightest 
are called Venus, Mars, Jupiter, and Saturn. It is thus 
seen that the earth is not a solitary body, unlike all 
others, but that it occupies an intermediate position in a 
large family of bodies. 

The sun and the planets form a group of bodies called 
the solar system. As the stars resemble the sun in many 
ways, it is believed that each star may be accompanied by 
a larger or smaller family of planets ; hence the number 
of earth-like bodies in the universe is probably very large. 

Age of the Earth. — It is impossible to say what the age 
of the earth and the solar system is, but it should be 
reckoned in millions and millions of years. There is every 
reason to believe that the sun and the planets existed for 
an indefinitely long time before the earth was inhabited by 



10 PHYSICAL GEOGRAPHY. 

plants and animals, and it is well proved that plants and 
animals lived upon the earth for a vast length of time 
before man appeared. It seems entirely possible that 
other planets than the earth may have once been, or may 
now be, occupied by inhabitants of some kind. 

As the solar system has existed for so long a time in 
the past, it may be expected to endure for an indefinitely 
long time to come. Even after the sun has lost its heat 
in the remote future, the planets may continue to wheel 
around it, cold and lifeless. The part of a planet's exist- 
ence during which it is inhabitable by life of any kind is 
probably a relatively small fraction of the whole. It is 
well that man, whose power over the other occupants of 
the earth has come to be so great, should sometimes be re- 
minded that the time during which he has been the chief 
of its inhabitants covers a very small part of its history. 

The Shape and Size of the Earth. 

Shape of the Earth. — The people of savage races, 
when they think at all about the shape of the earth, 
generally believe it to be a great plain, broken by hills 
and mountains and surrounded by the sea ; for that is the 
appearance of the lands when seen from some high point, 
with mountains rising to greater heights, lowlands extend- 
ing to the seashore, and the ocean stretching beyond. 

The people of an ignorant race usually regard the place 
where they dwell as the center of the great earth plain. Of 
the ocean they know little ; its further parts are invisible and 
mysterious, and its limits are thought to be of a different 
nature from the safe and solid lands. 



THE EARTH AS A GLOBE. 



11 



Among the earliest observations that led to a knowl- 
edge of the true form of the earth are those made by 
Greek philosophers in the fourth century, B.C. It was 
noticed that in travelling a -few hundred miles north new 
groups of stars came in sight over the northern horizon, 
while stars that had been in sight over the southern hori- 
zon could no longer be seen. When travelling south, 
changes of the opposite kind were observed. It was 
therefore concluded that the 
surface of the earth must be 
convex instead of flat, and 
that the earth as a whole 
must, be a sphere. (See Ap- 
pendix A.) 

The great philosopher, 
Aristotle, who flourished 
about the middle of the fourth 
century, B.C., said that the 
earth must be a sphere be- 
cause when the earth's shadow 
falls on the moon, causing a 
lunar eclipse, the edge of the 
shadow is a curved line. He added that the earth cannot 
be a very large sphere, for otherwise the change in the 
position of stars with respect to the horizon would not be 
JO soon evident to one travelling north or south. 




Fig. 3. — Eclipse of the Moon, showing the 
Curved Edge of the Earth's Shadow. 



The familiar argument for the globular form of the earth, 
based ou the disappearance of the lower part of distant objects 
at sea, was not mentioned by ancient writers until about the 
beginning of the Christian era. 



12 PHYSICAL GEOGRAPHY. 

Size of the Earth. — The earliest recorded measure men 
of the size of the earth was made by a Greek philosopher 
in the third century, B.C., who showed its diameter to be 
about 8000 miles. (See Appendix B.) The knowledge 
thus gained by the ancients concerning the shape and size 
of the earth was afterwards forgotten for many centuries, 
and was not regained until about the time of Columbus. 
Since then voyages have been repeatedly made around the 
earth, and its size has been accurately measured. 

About two centuries ago it was discovered that the 
earth is not a perfect sphere, but is very slightly flattened 
at the poles. This was explained by Newton as a result 
of the earth's rotation, and it may be taken as one of the 
best proofs that the earth, and not the sky, turns round 
once a day. 

The distance from the earth's center to either pole is about 
thirteen miles less than to the equator. This is so little in a 
globe nearly 8000 miles in diameter, that if a curve were 
drawn to represent the polar flattening, the unaided ey« 
could not detect its difference from a circle. The most care- 
ful measurements make the distance from center to pole 
20,855,121 feet, and to the equator 20,926,062 feet. The 
avera2:e diameter of the R'lobe is 7912 miles. 




Origin of the Earth's Shape. — The eruption of hot lavas 
from volcanoes supports the belief that the inner part of 
the earth is so hot that the rocks there would yield 
they were pressed more in one direction than in anoth 
If the earth ever had an irregular shape, the higher pa: 
would sink down on the yielding interior, and the lower 
parts would be bulged out until the form became globular 
and the pressure was everywhere balanced. 



oi 




THE EARTH AS A GLOBE. 13 

■ Even if the entire earth were as cold as its outer part 
(commonly called the crust), it could not preserve a very 
irregular shape, for its inner rocks would not be strong 
enough to withstand the unequal pressures that would exist 
beneath the higher and lower parts. 

But even if cold and rigid from surface to center, an irregu- 
lar form could not endure ; for the surface rocks would decay 
and crumble under the attack of the weather, and the loose 
rock waste thus formed would be washed from the heights 
into the hollows. The earth is so old that, whatever shape 
it may have once had, and however cold and rigid its rocks, 
it would long ago have been worn nearly smooth and 
round. 

It will be seen in a later chapter that all the higher parts 
of the lands to-day, plateaus, mountains, and volcanoes, have 
gained their height late in the earth's history. It may be 
hundreds of thousands of years since they were formed, but 
they are nevertheless young in the earth's measure of time. 
If it had not been for the various forces by which the shape 
of the earth's crust has been slightly changed, raising plateaus 
and building mountains here and there, now and then, in its 
long history, the surface of the earth would be much smoother 
than it now is. 

Consequences of the Size and Shape of the Earth. — The 

earth is so large that savage peoples, even on the same 
continent, may remain for centuries in ignorance of each 
other. Each people comes to have its own way of doing 
things appropriate to its surroundings. Thus differences 
f language and customs have originated. But since rail- 
ads and steamships have been invented by civilized 
]|eople in modern times, the earth may be considered a 
relatively small planet. An active traveller may visit 
nearly all its larger districts in his adult years. 



14 



PHYSICAL GEOGRAPHY. 



The civilized nations liave become well acquainted with 
each other. They now maintain an international postal 
service, by which nearly 200,000 post-offices are placed 
in communication with each other. The Roman alpha- 
bet is used by many nations, although their languages 
may be different. The use of Arabic numerals is 
even more extended. The metric system of weights 
and measures is already widely introduced, and will 
probably be adopted by all advanced nations in the 
twentieth century. 

Althougli the entire earth is large, if compared with the 
size of a single state, the people of many distant countries 
sell their home products to each other. The products of 
remote regions are thus exchanged, even from as far as the 
opposite sides of the earth. The wheat of one country fur- 
nishes flour to another. Australian wool and meat are sold 
in the markets of London. A. voyage round the world has 
come to be regarded as hardly more than a pastime. 

Although the lands have many mountains and valleys, 
the general surface of the continents and oceans does not 
depart greatly from the form of a smooth globe, as shown 




100 MILES 

Fig. 4. — Height of Land and Depth of Sea compared to Curvature of Earth's Surface. 

in Fig. 4. This is most fortunate, for on a very unevei 
and irregularly shaped earth long ascents and descents be 
tween the higher and lower parts would make travel am 
transportation enormously difficult and sometimes utterly 
impossible. 



THE EABTH AS A GLOBE. '15 

It is the attraction of the earth, or terrestrial gravity, 
that causes bodies to have weight and to fall when not 
supported. Recognizing the earth to be a globe, " down " 
is towards its center, in the direction that bodies are pulled 
by its attraction; "up" is away from the earth's center, 
or against the pull of gravity. A level surface, like that 
of a body of water at rest, is at right angles to up-and- 
down, or vertical, lines. 

The curved surface of the ocean is level, for it is every- 
where at right angles to the direction of gravity. 

It has been proved by experiment that the stems and 
trunks of plants grow " up," because the force of gravity acts 
downward. Even on hillsides trees tend to grow erect, and 
not square out from the sloping surface. Branches, like those 
of the spruce, that turn upward when young often droop 
when old, owing to the long-continued action of gravity. 

Many parts of the skeleton of man and animals, as well as 
many of the muscles of the body, are especially developed to 
bear the strain that is exerted upon them by the downward 
weight of the body. The habit of lying down to sleep has 
been formed partly in order to rest the muscles that are in 
action while standing. 

The Earth's Rotation and its Consequences. — The turn- 
ing, or rotation, of the earth on its axis from west to east 
gives us the impression that the sun, moon, and stars 
move around the earth from east to west. One may gain 
a false impression of the same kind while looking from 
the window of a smoothly running train, when it may 
almost seem as if the landscape moved backward instead 
of the train forward. 

The succession of sunlight and darkness, or day and 
night, has given man and many animals the habit of 



16 PHYSICAL GEOGRAPHY. 

working by day and resting by night. The period of the 
earth's turning furnishes a natural unit of time, easily 
recognized and counted, and everywhere constant. 

Clocks and watches are regulated so as to keep time with 
the turning of the earth. The hour hand turns once for the 
average time of daylight and once for the average time of 
darkness. 

The rotation of the earth, causing sunrise and sunset, 
suggests a natural system of directions even to many sav- 
age tribes. The cardinal points, east and west, north and 
south, are in a general way recognized by most people of 
the world. 

The sun rises through the eastern half of the sky during 
the morning and sinks through the western half of the sky 
in the afternoon. Midday is the moment when the sun passes 
the north and south line that divides the eastern from the 
western half of the sky. The sun then reaches the greatest 
height above the horizon ; and hence at this moment a verti- 
cal rod casts the shortest shadow. 

Consequently, a true north line may be determined by 
noting the direction of the shortest shadow cast by a vertical 
rod. The north line thus determined would, if followed, lead 
to the north pole ; a line in the opposite direction, to the south 
pole. All such lines are called meridians, or midday lines. 
When continued they form circles running around the globe 
and intersecting at the poles. 

Lines drawn at right angles to the meridians run east and 
west. Such lines form circles parallel to one another, never 
intersecting ; they are therefore called parallels. The parallel 
that lies midway between the poles is called the equator, 
because it divides the earth into equal parts, called the north- 
ern and southern hemispheres. 



THE EARTH AS A GLOBE. 



17 



J^ovf'i^fc 



A network of meridians and parallels may be in imagi- 
nation drawn upon the earth's surface so as to divide it 
in a regular manner with relation to the poles and equator. 
It is in reference to these lines 
that directions are accurately de- 
fined and the relative positions 
of various points determined by 
explorers and surveyors. Thus 
great advantage is taken of the 
simple globular form and of the 
regular rotation of the earth. 




\\ \ \ PIxrallel / 



^outh i'ul" 



Fig. 6. — Meridians and Parallels. 



Land surveys, by which the 
boundary lines of farms and house 
lots are marked out, are best made 
with reference to the local meridian. Navigators constantly 
have occasion to determine their position with respect to the 
network of meridians and parallels, in order to avoid islands 
and headlands and to reach their desired ports. (See Ap- 
pendix C.) 

The boundaries of thinly settled parts of civilized nations 
and states are often defined by -meridians and parallels, as 
between the western parts of the United States and Canada, 
as well as between many of the states themselves, and between 
the various parts of Canada and of Australia. 

(Further account of the earth as a globe is given in the 
Appendices C, D, E.) 



CHAPTER HI. 
THE ATMOSPHERE. 

The Relation of Man to Climate. 

The Bedouins of the Sahara. — The uplands and low- 
lands of a great part of northern Africa receive so little 
rainfall that their surface is dry and barren, forming the 
great desert of Sahara. Cultivation of the ground is 
impossible, except close to the dwindling streams, which 




Fig. 6. — Bedouins of the Sahara. 



wither away as they flow from the higher ground where 
most of the little rain falls. Nearly all the region is unin- 
habited, — a desolate waste of rock, stones, and sand, — 
but here and there the under soil in the low ground is 
moist enough to support a scanty growth of grass, which 
gives subsistence to the horses and camels of the wander- 
ing tribes of Bedouins. These people must frequently 



THE ATMOSPHERE. 19 

move from place to place to avoid, starvation; hence they 
do not build houses, but live in tents that can be easily- 
carried about as they wander from one pasture ground to 
another. As a result of their wandering habits, they 
have come to be excellent horsemen and show great 
endurance in surviving the hardships that they must 
often suffer. But, on account of being nearly destitute, 
they have the habit of taking what they want from any 
passing travellers whom they can plunder. They have 
thus preserved into modern times a rude manner of life 
that must have been universal in the early history of 
mankind, but that has been given up in recent centuries 
by the people of more advanced nations, where theft is 
now punished as a crime. 

One might expect that the Bedouins, on learning some- 
thing of the rest of the world from the traders of passing 
caravans, would wish to leave the barren Sahara for more 
fertile lands. On the contrary, so accustomed are they 
to a wandering life that they have no desire to change it. 
They persevere in the miserable conditions of the desert, 
content with their own ways and disliking the intrusion 
of strangers. Their manner of living is, like that of the 
Dwarfs in the equatorial forests and of the Eskimos in 
Greenland, another example of the great influence that 
climate exerts on the habits and customs of mankind. 
Just as the warm and moist climate of the equatorial forest 
and the frigid climate of Greenland are natural results of 
the form and rotation of the earth, so the dry climate of 
the Sahara is a natural result of the movements of the 
atmosphere on the rotating earth, warmed around the 
equator by a hot sun. 



20 PHYSICAL GEOGRAPHY. 

Climate and Commerce. — The growth and distribution 
of plants are controlled by temperature and rainfall. Tea, 
coffee, cane-sugar, cotton, and bananas are the products of 
plants that flourish best in a warm and rather moist cli- 
mate. The less intelligent peoples of the cooler and drier 
parts of the world know nothing about these useful pro- 
ducts, and use something else in their place ; but the more 
intelligent peoples of such regions, once having learned 
how valuable these plant products are, take great trouble 
to procure them. An important part of commerce is the 
traffic in articles of food raised in distant parts of the 
world. Tea is carried overland from China to Russia; a 
railroad now in construction will soon make this trade 
more active. Great cargoes of tea are shipped from China 
and Japan to our Pacific ports, and then sent forward in 
long freight trains over the mountain passes to the prairies 
and the eastern states. Steamships run from the West 
Indies to our Atlantic ports, laden with tropical fruits. 
The cotton crop of the southern states has been for many- 
years their most valuable product. All of it was formerly, 
and most of it is still, sent to the mills of Old and New 
England, where thousands of persons gain a living by 
spinning thread and weaving cloth; but in recent years 
some of the crop has been manufactured in southern mills. 
Many articles of clothing, the sails of ships, and the tents 
of armies are made from the cotton fiber. New inventions 
often increase the demand for the cloth and promote the 
cultivation of the cotton fields ; none being more notable 
than the bicycle, whose rubber tires have a layer of cotton 
duels:. Thus the climate, the commerce, and the industries 
of the world are intimately associated. 



THE ATMOSPHERE. 21 

Effects of Weather Changes. — Even temporary weather 
changes may be of great importance when the ordinary 
variations of temperature, rainfall, and wind are exceeded. 
In summer hot winds blowing from the southwest some- 
times blight the crops of Kansas and Nebraska. In winter 
cold winds occasionally sweep down from the northwest 
and carry freezing temperatures as far as Florida, ruining 
the orange crop. Unusual drought may injure the growth 
of wheat, as during the winter and spring of 1898 in 
California. Excessive rains may flood the lowlands near 
the greater rivers, as along the lower Mississippi in the 
spring of 189T, when an area of 13,000 square miles (as 
much as that of Massachusetts and Connecticut, and 
more than that of all Belgium) was overflowed, and the 
destruction of live stock and crops caused losses exceed- 
ing $12,000,000. Violent winds may beat down the 
cornfields in their path, and the loss thus occasioned on 
a farm may prevent the purchase of better farming 
machinery for the next year. Storms at sea may help to 
turn the course of history, as when a gale aided in dis- 
persing the Spanish " Armada " on the British coast in 
1588, during the reign of Queen Elizabeth. 

The harmful happenings of wind and rain are not to be 
prevented ; but it is possible that the injury they sometimes 
cause may be lessened when their coming is better fore- 
told, and when protection against their dangers is better 
planned. The prediction of cold winds by the Weather 
Bureau often gives farmers and merchants warning in 
time to guard their property against freezing. Irrigating 
canals, leading water from streams out upon dry fields, 
decrease the dangers of droughts ; famines are thus averted 



22 PHYSICAL GEOGEAPHY. 

in the great population of India. Dikes built near the 
banks of rivers prevent their overflow; the twentieth cen- 
tury may see the Mississippi thus controlled, as the Rhine 
has been controlled in the nineteenth century. Storms at 
sea have lost more than half their dangers, partly because 
sea-going vessels are now much stronger than formerly, 
partly because the movements of storms are now better 
known, so that their coming can be foreseen and their 
greatest fury avoided. An early navigator might have 
steered his vessel into the midst of a hurricane ; the mod- 
ern sea captain has been taught how to turn to one side 
of its probable course. 

Weather changes are by no means always unfavorable. 
An early spring, a warm summer, and a sufficient rainfall 
promote an abundant harvest; and in such a season of 
plenty the farmer receives a good return for his labor. 
He is then enabled to carry out improvements in his farm 
buildings, to clear and plow new fields. Years of pros- 
perity are thus connected with years of good weather, and 
great as well as small events are influenced by them. 

The Atmosphere. 

The Atmosphere is a light and transparent mixture of 
gases known as air. It rests on the lands and seas, 
forming the outermost part of the earth. Many processes 
that take place on the surface of the lands and seas result 
from the action of the atinosphere. The waves and cur- 
rents of the oceans are caused by the winds ; the soil that 
covers the greater part of the lands results from the decay 
of the underlying rocks chiefly through the chemical 



THE ATMOSPHERE. 



23 




action of moist air. Rainfall, so important in many ways, 
is entirely supplied by moisture carried from the oceans 
by the movements of the atmosphere. 

The atmosphere far overtops the highest mountains. Me- 
teors, or "falling stars," — small scraps of matter dashing 
toward the earth from distant space, — some- 
times burn at heights of over a hundred miles, 
showing that some air reaches that great altitude. 

Cloud, haze, and dust make the lower air tur- 
bid, and often cut off a great part of the sui 
rays; but when the atmosphere is clear, even tl 
faint light of stars penetrates its entire depth. 

Pressure of the Atmosphere. — Although t] 
air is invisible, it is attracted by the earth ai I 
exerts a pressure on the surface upon which 
rests. This pressure is about a ton on a squa 
foot. The pressure on a man's body amouni 
to several tons ; but this is not felt, because tl 
air within the body exerts a correspondii 
pressure outward. The air is so easily mov( I 
that little resistance is noticed when walkir 
through it, but fast trains on railroads a 
much impeded by the resistance of the a 
that they have to push aside. 

The pressure of the atmosphere is determini 1 
by the barometer, in which the air pressure 
balanced by that of a column of mercury about 
thirty inches high. The ordinary changes of 
atmosphei^ic pressure, such as accompany changes ^'e- ''■ 

of weather, are seldom more than a fifteenth of 
the total pressure. If a barometer is carried up a mountain, 
leaving much of the atmosphere beneath it, the pressure of 




24 PHYSICAL GEOGRAPHY. 

the overlying atmosphere is found to be much reduced. An 
ascent of a thousand feet causes a lowering of about an inch 
in the barometric column. Even the slight loss of pressure 
caused by going from the ground floor to the top of a build- 
ing is easily recognized with a good instrument. 

Although very light, the air supports the flight of birds 
and insects. The wind drives sailing vessels and windmills ; 
it carries about myriads of germs and pollen grains, as well 
as particles of mineral dust. In dry regions, where the land 
is not covered with vegetation, the shape of the surface is 
changed by the long-continued action of the wind in drifting 
sand and dust from place to place. 

Air is extremely elastic, changing its volume with every 
change of pressure. Its lower part is compressed by the 
weight of the overlying part, so that a cubic foot of air 
at sea level weighs about 0.075 pound, while at three 
miles above sea level its weight would be only half as 
much; and at an altitude of a hundred miles the air must 
be almost imperceptible. 

Men and animals living on high plateaus have become 
accustomed to the rarity of the air around them. There are 
villages on the plateau of Tibet where the density of the air 
is little more than two-thirds that at sea level. Mountain 
climbing above altitudes of 20,000 feet is almost impossible 
from the difficulty of breathing the thin upper air. 

It is by slight wave-like movements in the air that sound 
is transmitted. So easily is the air disturbed that a locust 
(cicada) may set hundreds of tons of air vibrating perceptibly 
to our nerves of hearing. When the volcano Krakatoa, be- 
tween Java and Sumatra, exploded in August, 1883, sounds 
were heard for 3000 miles, and atmospheric waves, detected 
by slight changes of pressure in barometers, passed three 
times round the earth. 



THE ATMOSPHERE. 25 

Composition of Air. — Air consists of a uniform mixture 
of gases, in wliich a small and variable quantity of water 
vapor is usually present. The gases are nitrogen, about 
four-fiftlis ; oxygen, about one-fifth ; argon, carbonic acid, 
krypton, and some others, each a hundredth or less. 

Nitrogen is found , in much larger share in the air than in 
all the rest of the earth, but it does not seem to be actively 
useful. Argon and krypton, recently discovered, are at present 
known only in the atmosphere. 

Water vapor, originally supplied by evaporation from the 
oceans, is the source of rainfall and the supply of all streams. 
The air feels damp or dry according to the amount of water 
vapor that it contains. When damp in hot weather, the air is 
sultry and uncomfortable ; when damp in cold weather, it is 
chilly and disagreeable. The same temperatures would be 
much more easily borne if the air were dry. 

All plants and animals take in air and use some of its 
oxygen to combine with part of their substance in a very 
slow combustion, which produces a slight amount of heat 
but no fire. Thus all forms of life, animal and vegetable, 
gain the energy with which they are enabled to perform 
their life work. 

Plants do much less work and use much less oxygen than 
animals. The process of taking in a portion of air and giving 
out the unused part along with the products of the slow 
internal combustion (water vapor and carbonic acid) is called 
respiration, or breathing. It continues day and night. The 
organs of respiration differ greatly in different forms of life, 
but the process is much alike in all. 

Fire is the result of an active combination of some combus- 
tible substance with the oxygen of the atmosphere. The heat 
thus developed may convert water into steam, and the expansive 



26 



PHYSICAL GEOGRAPHY. 



force of the steam may be used to drive engines and many 
kinds of machinery. 

Carbonic acid, although a small part of the atmosphere, 
is of great impor- 
tance as the chief 
food of plants. It 
is taken in by the 
green cells and de- 
composed under 
the action of sun- 
light, part of it 
(carbon) being re- 
tained to unite 
with the sap and 
form the tissue 
of the plant, part 
(oxygen) being 
given out again. 




Fig. 8. 



Grizzly Bears suffocated in Death Gulch, 
Yellowstone Park. 



Carbonic acid is suffocating if present in much larger 
quantity than usual. It is given forth from the ground in 



Fig. 9. — Direct and Oblique Says. 



certain parts of the world, as in Death gulch, Yellovt^stone 
Park. Grizzly bears often lose their lives in this ravine. 



THE ATMOSPHERE. 



27 



Temperature of the Atmosphere. — ^The temperature of 
the land and sea surface and of the lower atmosphere is 
controlled by the sun's rays. Hence higher temperatures 
must prevail around the equatorial belt, where the sun 
shines more directly upon the earth's surface ; and areas 
of low temperature must be found around the poles, 
where the sun's rays are oblique, as shown in Fig. 9. 
Belts of stronger, medium, and 
weaker sunshine are thus de- 
fined, which are known as the 
torrid, temperate, and frigid 
zones. (See Appendix F.) 
Fortunately the cold or frigid 
areas around the poles occupy 
a relatively small part of the 
world. 

The temperature of the air 
may be measured by a ther- 
mometer suspended so as to be 
protected from direct sunshine 
and from rain or snow. If 
placed outside of a window, it should be on the north side 
of the building, where currents of warm air escaping from 
windows beneath cannot affect it. Some thermometers are 
arranged so as to give a continuous temperature record in a 
curve drawn on a sheet of paper ; such instruments are called 
thermographs, one pattern being shown in Fig. 10. 

The temperature of the air is not much affected by the 
direct action of the sun's rays ; it is controlled largely by the 
temperature of the land or sea surface on which the air rests. 
Zones of high and low temperature are therefore found in the 
lower atmosphere from the equator to the poles, but the upper 
atmosphere is everywhere cold. At the height of ten or more 




Pig. 10. 



- The Comey Self-Eecordlng 
Thermometer. 



28 



. PHYSICAL GEOGRAPHY. 



miles, the air above the equator is probably little warmer than 
that over the poles. 

Temperature Charts. — The distribution of the average 
temperatures for the year is shown on the chart of the 
world, Fig. 11. A line drawn near the earth's equator, 
through the middle of the belt of greatest heat, is called 




Fig. 11. — Chart of Mean Annual Temperatures. 

the heat equator, the average temperature of which is about 
80°. From the heat equator the temperature decreases 
toward each pole at the rate of about a degree of the 
Fahrenheit thermometer scale to a degree of latitude. 

The distribution of temperature on charts, such as Fig. 11, 
is indicated by lines drawn through places having the same 
temperature, and separating regions of higher and lower tem- 
perature. Fig. 12 gives the degrees of temperature prevailing 
over the middle and eastern United States on a certain morn- 
ing. The broken line is drawn so as to separate all places 



THE ATMOSPHERE. 



29 



-7-9 -<i> 



having higher temperatures than 40° from those having lower 
temperatures. Similar lines may be drawn for temperatures 
of 10°, 20°, 30°, 50°, and 60°. Such lines are called isothermal 
(equal temperature) lines, or isotherms. 

Circulation of the Atmosphere. — Cold air from the polar 
regions, being heavier than the warm lower air of the torrid 
zone, continually 
tends to creep under 
it ; and the warm air 
thus lifted up tends to 
overflow towards the 
poles. A permanent 
interchanging move- 
ment, or circulation, is 
thus established in the 
atmosphere between 
the warmer and colder 
parts of the earth. 
On account of the 
earth's rotation, the 
air currents, or winds, 
do not flow directly north and south, but are turned some- 
what to the east or west. (See Appendix G.) 

A circulation will be established by opening a door between 
two rooms, one warm and the other cold. The cold air will 
creep into the lower part of the warm room, while the warm air 
will spread into the upper part of the cold room. The move- 
ment may be shown by the drift of smoke from a smouldering 
match. If the cold air is warmed as it enters the warm room, 
and the warm air cooled as it enters the cold room, the circu- 
lation will continue indefinitely. 




Fig. 12. — niustration of an Isothermal Line. 



30 



PHYSICAL GEOGRAPHY. 




Planetary Winds. — The most important members of 
the atmospheric circulation on our planet may be briefly 
described as follows. The trade winds blow from about 
latitude 28° N. and g. 
obliquely towards the equa- 
tor, in the northern hemi- 
sphere from the northeast, 
in the southern from the 
southeast.^ The prevail- 
ing westerly winds blow 
from a westerly source, but 
with a slight inclination 
towards the pole, over the 
greater part of the tem- 
perate zones. The polar 
winds, occupying rela- 
tively small areas around each pole, are little known. 
Belts of light, variable winds and frequent calms lie 
between the several belts of steadier winds. All 
these are members of what may be called the planetary 
circulation. 

The trade winds are so called from the constancy with 
which they follow a steady or " trade " course. Their 
velocity is from ten to thirty miles an hour. They give 
fair weather, seldom interrupted by storms, and generally 
dry unless a mountain range rises across their path. Low- 
lands over which they blow are made desert by the drying 
action of their warm air. The African Sahara and the 
central Australian deserts are thus explained. 



Fig. 13. — The Planetary Circulation of the 
Atmosphere. 



1 Winds are named from the point of the compass from which they 
blow. 



THE ATMOSPHERE. 



31 



When sailing vessels enter the trade-wind belt, they may- 
count upon making good headway. If sailing with the winds, 
extra sails are often rigged out on the ends of the yards, and 
thus aided by a broadened stretch of canvas, the vessels speed 
along day and night. 

Where the trade winds encounter mountain ranges, they 
. are forced to ascend the .side on which they approach. As 
they rise the air expands, cools, and becomes cloudy and rainy. 
The eastern slope of the Andes about the headwaters of the Ama- 
zon, the mountains 
along the east coast of 
Brazil under the south- 
east trades, and the 
eastern slopes of the 
highlands of Mexico 
and Central America 
under the northeast 
trades, thus receive a 
good amount of rain- 
fall (80 to 100 inches 
a year). All these 
mountain slopes bear 
heavy forests. (See 
Appendix H.) 

The further slope 
of the mountains, where the winds descend, is relatively dry 
and barren, as on the western side of the Peruvian Andes. 

Even in the Sahara the few mountains that interrupt the 
general surface receive a sufficient rainfall to permit tree 
growth; but the streams supplied on the mountain sides 
wither away after descending to the lower desert. 

The prevailing westerlies are much less regular than the 
trades. They may weaken to less than ten miles an hour, 
or strengthen to gales of sixty miles an hour. They often 
shift from their general course to take part in irregular 




Fig. 14. 



- Wet-Weather Streams of the Tarso Mountains, 
Sahara. 



32 PHYSICAL GEOGBAPHY. 

movements, indicated in the temperate latitudes of Fig. 13. 
It is chiefly to these great whirl-like movements that the 
frequent changes of weather in temperate latitudes are due. 

The lands under the westerly winds are generally well 
watered, especially on bold coasts east of the oceans. Abun- 
dant rainfall is received on the mountainous Pacific slopes of 
North and South America in middle latitudes, but the oppo- 
site slopes are comparatively dry. In these latitudes the 
western slope of the mountains is heavily forested, while 
the eastern slope has an open tree growth, or none. The 
distribution of forests over the great American mountain sys- 
tem thus gives striking illustration of the relation of timber 
supply to winds and rainfall. 

The belt of calms and light breezes in the neighborhood 
of the equator, between the inflowing trade winds, is called 
the doldrums^ or equatorial calm belt. It is prevailingly 
cloudy ; rain falls every day or two, especially in the late 
afternoon or night. The lands are heavily forested under 
this warm and moist belt, and agriculture is difficult from 
the very luxuriance of vegetation. 

Sailing vessels bound across the equator are frequently 
becalmed for several days in the doldrums. They must then 
take advantage of every light breeze to push onward and reach 
the trade winds beyond. The dull sky, the sultry air, and the 
glassy sea make the delay all the more vexatious. 

The rain of the doldrums results from the slow ascent of 
the warm air supplied by the inflowing trade winds. The 
lower air is raised to greater and greater height by the inflow 
of more air beneath from both sides ; it expands as it rises, 
cools as it expands, becomes cloudy as it cools, and thus gives 
forth plentiful rain. Violent thunderstorms are frequently 
formed in the great cloud masses of the calm belt. 



< 



THE ATMOSPHERE. 



33 



An ill-defined belt of light breezes and occasional calms, 
known as the horse latitudes or tropical calm belt, lies in 
each hemisphere between the trades and the prevailing 
westerlies. Here the weather is generally fair and dry. 

The lower winds blow obliquely away from this belt on 
both sides, and air must descend from aloft to supply their 
currents. As the air slowly settles down, it is compressed by 
the weight of that which rolls in on top of it ; as it is com- 
pressed, it is warmed ; and as it is warmed, any clouds that it 
may have contained are dissolved ; hence clear, fair weather 
is prevalent in this belt. 

Storms of the "Westerly Winds. — The irregular winds 
by which the prevailing westerlies are so often interrupted 
sometimes have an in- 
ward, sometimes an out- 
ward, spiralling move- 
we?i^,asinFig.l5. They 
are like great, slow- 
turning whirls, 500 to 
1000 miles in diameter. 
When blowing outward, 
the winds are light and 
the weather is fair. 
When blowing inward, 
the weather is cloudy 
and wet, and the winds may gain a stormy strength, 50 
to 80 miles an hour on land, and sometimes over 100 
miles an hour at sea. 

Both classes of whirls travel 500 to 1000 miles a day 
in an easterly direction, with the general drift of the 
atmosphere in temperate latitudes. They may strengthen 




Fig. 15. — Spiral Wind Courses. 



34 



PHYSICAL GEOGRAPHY. 



and increase in area for a time, then weaken and fade 
away; their duration being from a few days to two or 
three weeks, and their distance of travel from 5000 to 
15,000 miles. 

The great whirls in the westerly winds are well shown 
on the daily weather maps published by the U. S. Weather 
Bureau, from which Figs. 26 to 29 are reduced. The direc- 
tion in which the whirls turn in the northern hemisphere is 
opposite to that in the southern. 




Fig. 16. — Isotherms for January. 

The pressure of the atmosphere is less tlian usual about 
the central part of the inward whirls, and greater than usual 
in the outward whirls. Hence they are often called low- 
pressure and high-pressure areas. They have also been 
named cyclonic and anticy clonic areas from the curving 
movement of their winds. 

The small and very destructive whirling storms, commonly 
called cyclones in the United States, are better named to7'- 
nadoes. Their winds probably reach a velocity of 200 miles 



THE ATMOSPHERE. 



35 



an hour. Tliey should not be confused with the large, slow- 
whirling cyclonic areas here ^escribed. 

Change of Seasons. — The earth moves around the sun 
once a year. For six months in each year (March 20 to 
September 22, or September 22 to March 20), one hemi- 
sphere receives a greater amount of sunshine than the 
other ; it may then be called the summer hemisphere, while 
the other is called the winter hemisphere. (See Appendix F.) 




Fig. 17. — Isotherms for July. 

During the summer half-year the heat equator moves a 
moderate distance from the geographic equator into the 
summer hemisphere, the high temperatures of the torrid 
zone advance towards middle latitudes, and the ligor of 
polar cold is lessened. In the Avinter half-year the j)olar 
cold is extreme, low temperatures advance over the middle 
latitudes, and the heat on the border of the torrid zone is 
tempered. 



36 PHYSICAL GEOGEAPHY. 

Ill both hemispheres the succession of higher and lower 
temperatures during the year produces the change of seasons. 
The winter months in tlie nortliern hemisphere are December, 
January, and February (these being the summer months of 
the southern hemisphere) ; the spring months are March, 
April, and May ; the summer months, June, July, and Au- 
gust; the autumn or fall months, September, October, and 
ISTovember. 

The change of temperature with the seasons is much less 
marked in the torrid zone than nearer the poles. In the 
temperate zone the summer half-year is the time of plant 
growth, and is therefore the season of greater activity in all 
industries immediately, connected with agriculture. 

One of the most interesting consequences of the advance 
of summer temperatures into higher latitudes is the passage 
of migratory birds, familiar to every lover of outdoor nature. 
The approach of winter is accompanied by the return of the 
birds to warmer latitudes. 

Terrestrial Winds. — The strength of the planetary 
winds and the boundaries of their belts vary with the 
seasons, as shown in Fig. 18. Thus modified, the winds 
may be called terrestrial, as belonging to the earth rather 
than to j)lanets in general. In the winter heraisphere the 
difference of temperature between equator and pole is 
strengthened, and the velocity of the winds is therefore 
increased. This is especially true of the prevailing west- 
erlies, where winter is the stormy season. The trade winds 
show a less distinct seasonal change of strength. 

The tropical calms move toward the equator in winter 
and toward the pole in summer (ST^ Fig. 18). Any 
country over which the calms migrate will have the west- 
erlies and their storms in winter, and the drying trades in 
summer. 



THE ATMOSPHERE. 



37 



This is the case Avith southern California, central Chile, 
and the Mediterranean countries of southern Europe and 
northern Africa. These countries are said to have a sub- 
tropical climate. 

As countries in the subtropical belts are dry in the growing 
season, agriculture generally requires the aid of irrigation 
(watering the fields by canals led from streams or reservoirs). 
The same is true of regions traversed by winds that have just 
crossed a mountain range, as in the western interior of the 
United States. 

The calms and rains of the doldrums migrate north and 
south with the lieat equator. The regions of rainfall thus 
controlled form the subequatorial belts (SQ, Fig. 18). 




Fig. 18. — Diagrams of Terrestrial Winds for January and July. 

The plains of the Orinoco in Venezuela receive a plentiful 
rainfall in July and August, but in December and January 
they are relatively dry. In the wet season cattle find abun- 
dant pasture on the uplands ; in the dry season they are driven 
into the valleys. On the plains between the headwaters of 
the Amazon and Parana, the months of wet and dry seasons 
are reversed from those of "Venezuela (Figs. 19 and 20). 



38 



PHYSICAL GEOGEAPHY. 



The Sudan, between the Sahara and the equatorial for- 
ests of Africa, is a region of summer rains, with open tree 
growth or grassy plains. The western Sahara, between the 
reach of the subtropical (winter) rains on the north and the 
subequatorial (summer) rains on the south, gives no important 
river to the Atlantic along a thousand miles of coast line. 
The rise of the Nile in Egypt from June to September results 
from the northward advance of the equatorial rains over the 
upper part of its basin, as in Fig. 20. 

Another remarkable result of the migration of the doldrum 



kr^^"^^^:rv-. 



■Ov f -e T o =5 ''r^ v"^ \ w 





EST^ERLY WIND 



North! !^r~s T > t r a d \ e / n /n 

^1 .^ \ Ll/. 







O =! f." Y 



"^X-V'/r X>^/iVG- * "r "- 'l'(f - 




Fig. 19. — winds of January. 

belt is seen in the change in the direction of the trade winds 
when they cross the geographic equator on the way to the 
heat equator (Figs. 18 to 20). The northeast trade is extended 
into a northwest wind in the southern summer, the south- 
east trade into a southwest wind in the northern summer. 
Thus on both sides of the equator, in the narrow subequatorial 
belts where this relation appears, the winds alternately blow 
from opposite directions as the seasons change. Winds of 
this kind are called monsoons. 

Tropical Hurricanes. — Thunderstorms are of frequent 



THE ATMOSPHERE. 



39 



occurrence in the doldrums over the oceans. When the 
doldrum belt migrates to its furthest distance from the 
equator, north or south, larger storms with whirling winds, 
known as hurricanes or tropical cyclones, are occasionally 
developed, as if from overgrown thunderstorms. 

After being started in the doldrums, hurricanes travel 
along a curved path near the western border of the ocean, 
and in a week or two reach the temperate zone, increasing in 
size, but generally decreasing in violence as they advance. 




Fig. 20. — Winds of July. 



Formerly great destruction was wrought on vessels at sea by 
these storms ; but now that the season of occurrence (late 
summer), the usual path, and the behavior of the winds of 
hurricanes have been learned, and now that vessels are built 
larger and stronger, losses at sea are much less serious than 
they were a century ago. 

When hurricane winds blow over islands in the torrid ocean, 
they may cause much damage to vessels in the harbors by 
driving them ashore ; and to settlements by destroying their 
plantations. Cocoanut palms may thus be stripped of their 



40 



PHYSICAL GEOGBAPET. 



grgat leaves, after which they require a number of years of 
growth before again bearing the fruit of which so many 
uses are made. 

Irregular Development of the Terrestrial Winds. — The 
irregular arrangement of land and water pi-events the 
regular development of the terrestrial wind system, and 
gives rise to certain changes in wind direction over each 
ocean and continent. 

The heat equator generally stands north of the geographic 
equator over the Pacific Ocean, especially over its middle and 
eastern parts. (This is chiefly because more cold water is 
brought towards the equator by ocean currents from the south 
than from the north.) During the northern summer a south- 
west monsoon is imperfectly developed within the northern 




Fig. 21. — Winds of the Atlantic Ocean in January and July. 

subequatorial belt of the Pacific ; during the southern sum- 
mer a northwest monsoon makes its appearance only in the 
western part of the southern belt (Fig. 19). 

In the Atlantic also the heat equator is prevailingly north 
of the geographic equator. (This is for the same reason as 



THE ATMOSPHERE. 41 

in the Paci^c.) The southeast trade wind is extended into the 
northern subequatorial belt during the northern summer ; but 
the northeast trade wind does not reach the corresponding 
southern belt during the southern summer. 

The continents lie somewhat across the paths of the 
terrestrial winds, and interfere with their regular flow. 
Hence branch winds connect the trades and the wester- 
lies, and great wind eddies blow more or less distinctly 
around each ocean basin, especially in the summer hemi- 
sphere, as in Figs. 19 to 21. 

The North Atlantic wind eddy is so distinct that the Pyr- 
enees and Atlas mountains are more rainy on their northern 
than on their southern slopes. On the Pacific West of North 
and South America the eddying winds blow towards the equa- 
tor across the subtropical belts. 

Annual Range of Temperature. — The air over the lands 
is warmer in summer and colder in winter than that over 
the oceans in the same latitudes. Places in the interior 
of continents, therefore, have a much stronger change of 
seasons than those on continental borders or on islands. 

The difference between the average temperatures of the 
warmest and coldest months is shown in Fig. 22. It is gen- 
erally less than 10° over the torrid oceans, and less than 20° 
over most of the temperate oceans. On land the range is 
stronger. Central Australia and the interior of the Sahara 
have a range of over 30°. Over most of the United States 
the range reaches 30° to 60° ; over a belt of land from Hud- 
son Bay into Alaska the range is more than 80°. Over the 
greater part of Europe- Asia the range exceeds 40° ; and in 
northeastern Siberia it exceeds 100°. 

In regions of the greatest range the winters are so cold 
that the ground is frozen to a depth of 100 feet or more. In 



42 



PHYSICAL GEOGRAPHY. 



winter ice is so hard that the runner of a skate does not hold 
upon it ; wood is too hard to be chopped with the axe. In 
summer thawing reaches only a few feet below the surface. 

As the air over the continents is alternately warmer and 
colder than that over the surrounding oceans, the winds 




XINE3 OF 

EQUAL ANKCAL KANGE 
OF TE31PERATCRE, ^ 



Fig. 22. — Chart of Equal Annual Range of Temperature. 

tend to blow inward towards continental centers in sum- 
mer, and outward from them in winter. The terrestrial 
circulation is much complicated by this tendency. 

In winter, when the winds tend outward from land to sea, 
the far inland regions have much dry and clear weather ; in 
summer, when winds blow inward, the lands have a greater 
share of clouds and rain. 

The summer inflow from sea to land strengthens the wind 
eddies on the western side of the oceans. For example, in 
July and August a prevailing southerly wind blows from the 
Gulf of Mexico up the Mississippi valley, increasing the rain- 
fall of the region that it reaches. In winter the outflow from 



THE ATMOSPHERE, 



43 




Fig. 23. — Monsoons of Northern Sanimer. 



the continent tends to counteract the eddy ; at that season 
the winds of the Mississippi valley are prevailingly from a 
northern source, and 
the rainfall is light. 

Southern and 
eastern Asia ex- 
hibit these features 
on a large scale. In 
summer the winds 
blow obliquely 
towards the con- 
tinent from the 
Indian and Pacific 
oceans, giving a heavy rainfall on the more mountainous 
slopes. In winter the winds blow obliquely outward from 
the continents, and the lands are then relatively dry. 
These changing winds are known as the Asiatic monsoons. 

The monsoons of 
the Indian Ocean are 
the most remarkable 
of the world. In 
the northern sum- 
mer (Fig. 23) they 
seem to be a great 
extension of the 
southeast trades, 
turned into a south- 
west wind after 
crossing the equa- 
tor, and becoming somewhat irregular in direction on reaching 
the lands. In the southern summer (Tig. 24) the northeast 
trade wind not only occupies its usual belt, but appears to be 
extended across the equator into the southern hemisphere, 




Fig. 24. — Monsoons of Southern Summer. 



44 PHYSICAL GEOGRAPHY. 

where it is turned to a northwest wind. The primitive sailing 
vessels of the Indian Ocean in earlier centuries, poorly adapted 
for sailing against the wind, made voyages only as the monr 
soons favored their courses, — going outward from India to 
Africa in one half-year, and returning in the next. 

The east coast of the Malay peninsula is beaten by heavy 
surf under the northeast monsoon, and then the native fisher- 
men stay ashore. But under the southwest rnonsoon, an off- 
shore wind, the water is comparatively smooth, and large fleets 
of fishing boats put out to sea with their palm-leaf sails. 

Winds on Land. — The winds are not so strong or so 
regular on the uneven lands as on the level seas. In val- 
leys the winds are much influenced by the direction of the 
enclosing slopes. Hence observers in a rugged country 
may often recognize the general direction of the winds 
better by watching the drift of the clouds than by noting 
the position of their wind vanes. 

The air over the lands is cooler and heavier than that 
over the sea at night, but warmer and lighter by day. 
Hence the wind tends to blow alternately off and on shore 
on many coasts, such winds being known as land and sea 
breezes. 

On the coasts in the torrid zone the sea breeze is welcome, 
as it tempers the excessive heat of the day on land. The 
same is true of summer weather in the temperate zone. On 
the coast of Peru the fishermen sail off shore in the morning 
with the land breeze, and return in the afternoon with the sea 
breeze. 

Daytime winds. — In fair, warm weather the lower air 
lying on the land becomes unduly heated by day, as compared 
to the overlying air. Overturnings are thus produced, and 
the faster-moving currents from aloft are brought down to 



THE ATMOSPHERE, 45 

the surface. Hence on land the winds of daytime are com- 
monly stronger than those of the night. This is prevailingly 
the case through the year on torrid lands ; it is characteristic 
of summer weather in the temperate zone, but is less noticed 
in winter. At sea no such daily change in the strength of 
the wind occurs. 

Rainfall. — Rain, snow, hail, and sleet are all included 
under the general term rainfall. The explanation already 
given of the winds has shown how closely the amount and 
season of rainfall are connected with the circulation of the 
atmosphere. It is largely in this way that the prevailing 
winds are important in controlling the distribution of 
vegetation, and thus of population. 

Snow is formed when the moisture of the air is condensed 
at temperatures below the freezing point (32°). Rain occurs 
when the moisture of the atmosphere is condensed into drops 
at temperatures above the freezing point, or when the snow- 
flakes of lofty clouds descend into the warmer lower atmos- 
phere, where they melt before reaching the ground. Sleet 
is half-melted snow. Hail occurs chiefly in summer, when 
the ascending air currents of lofty thunderstorms carry rain- 
drops so far upward that they are frozen before they fall. 
(See Appendix H.) 

The amount of rain is determined by measuring the depth 
of water that is collected in a vessel having vertical sides, 
called a rain gauge. Snow should be melted before it is 
measured. An annual total of 18, 20, or more inches is 
necessary for agriculture, as over the great prairie region of 
the Mississippi and Ohio valleys from the 95th meridian 
eastward. If the annual amount is between 18 and 10 
inches, agriculture requires irrigation, as on a large part 
of the Great Plains east of the Rocky mountains, and 
over large areas in the basins of Utah and Nevada; but 



46 



PHYSICAL GEOGRAPHY. 



scattered grass sufficient for cattle ranges may grow in such 
regions. If the annual total is under 12 or 10 inches, there 
will not be water enough for irrigation, unless it is supplied 
by a large river that rises in a moister climate, as in parts 
of Arizona and southeastern California, 

The distribution of rainfall over the world, represented 
in Fig. 25, shows that the greater amounts occur in the 
subequatorial belts, and on mountain slopes ascended by 




Fig. 25. — Chart of Annual Kainfall. 

Dark shading, heavy rainfall (over 100 inches) ; medium shading, moderate rainfall ; 
light shading and blank, light rainfall (generally under 20 inches). 

the trade winds or the prevailing westerlies. The dry and 
desert regions of the world are either lowlands of the 
trade-wind belt, like the Sahara and central Australia, or 
continental interiors crossed by the westerly winds. The 
greater part of western Europe and of eastern North 
America are fortunate in receiving a plentiful but not 
excessive rainfall. 

The heaviest rainfall in the world occurs on the southern 
slopes of the Himalaya, north of tlie Bay of Bengal. Here 



THE ATMOSPHERE. 47 

the rainfall of a single year would measure 35 or 40 feet 
in depth, and much more than half of this amount falls 
during the summer half-year when the southerly monsoon is 
blowing. On the bold southwest coast of India an annual 
fall of over 30 feet has been measured. 

In the polar regions the annual snowfall, melted, would 
seldom exceed 15 inches of water, and would frequently 
be less than 10. This is because the cooling of cold air does 
not condense much moisture from it. In the torrid zone the 
equatorial rains are heavier, because the cooling of warm air 
produces an -abundant condensation of moisture. 

Dew and Frost. ■ — Dew is a deposit of moisture on the 
ground, or on loose objects like leaves and sticks lying on 
the ground. It is formed when the ground becomes cool 
enough at night to chill the air near it so as to change some 
of the water vapor that it contains into the liquid form. 

The temperature at which dew begins to be formed is called 
the dew point. It may be determined by experiment as fol- 
lows : half fill a tin cup with water whose temperature is 
about like that of the air. Then slowly pour in ice-water, 
stirring it with a thermometer. When the outer surface of 
the cup is clouded by a deposit of moisture, the temperature 
of the water gives a close indication of the dew point. 

When moisture is condensed upon the ground at tem- 
peratures below the freezing point, it forms frost. Thus 
frost on the ground corresponds to snow in the air, and 
dew corresponds to rain. 

Dew and frost are in part supplied from water vapor in 
the air that lies near the ground, in part by vapor that rises 
through the soil from its deeper and moister parts. In the 
daytime the vapor from the soil escapes into the warm air ; 



48 PHYSICAL GEOGRAPHY. 

but at night, when the ground is colder at the surface than 
beneath, the rising vapor is condensed. Dewdrops found on 
the blades of grass and on the living leaves of plants close 
to the ground are in large part supplied by the water that the 
plants bring up from the ground through the roots. In the 
daytime the moisture evaporates from the leaves, but at 
night it may collect upon them in drops. 

Dew and frost are formed more abundantly on clear and 
calm nights than on cloudy and -windy nights ; for under 
the latter conditions the ground is not much cooled, while 
under the former conditions it may cool at night to a tem- 
perature 30° or 50° below that which it had under noon- 
day sunshine. 

Weather Changes. — The term weather includes all the 
atmospheric conditions that an observer may feel or see, — 
hot or cold, clear or cloudy, dry or wet, windy or calm. 

In the torrid zone the weather is marked by regular 
changes from day to night ; the changes are small at sea 
and greater on land, and they are seldom interrupted by 
storms. In the summer of temperate latitudes the same 
is largely true, although hot and cold periods give variety 
to the regular succession of day-and-night changes. In 
winter the weather of temperate latitudes is largely con- 
trolled by the passage of cyclonic and anticyclonic areas, 
which are then numerous and large, and the control by the 
change from day to night is relatively indistinct. 

In frigid latitudes the change of weather from day to night 
is always weak compared to the changes caused by the passage 
of the great atmospheric whirls. 

A comparison of the changes of local weather with the 
atmospheric conditions shown on the official United States 



THE ATMOSPHERE. 49 

weather maps discloses many problems of interest. (See 
Appendix I.) The summer season of the central and east- 
ern United States offers many examples of southerly 
winds, under whose influence the weather becomes warmer 
day after day, sometimes reaching an oppressive degree of 
heat. At the same time the day-and-night control is 
distinct, giving higher temperature, stronger wind, and 
greater cloudiness under the action of the sun than in 
darkness. Then, as the distribution of pressure is altered 
by the eastward drifting of cyclonic and anticyclonic areas, 
the wind changes to northwest, and the temperature falls 
for a few days to a moderate degree. 

In winter the irregular weather changes are stronger 
and more frequent than in summer. They may overcome 
the regular day-and-night changes. A mild spell of south- 
erly winds with cloudy weather near a cyclonic center 
may be quickly followed by a change to northwest winds 
and clearing weather, accompanied by a rapid fall of tem- 
perature to a low degree, this fall being known as a cold 
wave. 

The coldest winter weather usually occurs during 
periods of light winds or calms, under the influence of 
the central part of an anticyclonic area. The sky is then 
very clear, and the ground and the lower air are reduced 
to extremely low temperatures by cooling through the 
long quiet night. 

The changes of weather caused by the passage of a suc- 
cession of high and low pressure areas over the central 
and eastern part of the United States are illustrated in 
Figs. 26 to 29 for four successive days. 

At first the central area of low pressure, with rain and 



50 



PHYSICAL GEOGRAPHY 




Fig. 26. — Weather Map (first day). 



whirling winds, lies 
in western Iowa and 
Missouri, while clear 
or fair weather pre- 
vails over the Atlan- 
tic slope around an 
area of high pressure 
with outflowing 
winds. 

A day later the 
rainy area has 
reached the southern 
Great Lakes ; clouds 
are spreading east- 
ward as far as New 
England, while clear 
weather with northwest winds is extending from the Great 
Plains towards the Mississippi. 

On the third day the vsiiny area that at first lay over Iowa 
has reached the lower 
Great Lakes and the 
northeastern states ; 
a great extent of 
country in the Mis- 
sissippi valley and 
the southern states 
has clear and fair 
weather around a 
center of high pres- 
sure in western Ten- 
nessee, while a new 
area of clouds appears 
on the western plains. 
On the fourth day 
the first cloudy area 
has nearly disappeared in the northeast, and the second, with 




Fig. 27. —Weather Map (second day). 



THE ATMOSPHERE. 



51 




Fig. 28. — Weather Map (third day). 



its central low pres- 
sure, whirling winds, 
and rainy area, is ap- 
proaching the lower 
Mississippi; the 
region of clear and 
fair weather stretches 
from Minnesota to 
Florida, with a center 
of high pressure in 
North Carolina. 

The succession of 
weather changes pro- 
duced at any one 
place, as Washington 
or St. Louis, by the 
eastward passage of these areas of high and low pressure 
may be inferred from the diagrams. 

Changes of weather in the Mississippi and Ohio valleys 
are favored by the great extent of open plains from the Gulf 
of Mexico to the Arctic. The winds of cyclonic and anti- 
cyclonic areas are 
thus allowed free pas- 
sage from regions 
that, especially in 
winter, have very dif- 
ferent temperatures. 

In western Europe 
weather changes are 
not so strong or so 
frequent as in the 
central and eastern 
United States, but 
they are of the same 
general order. The 

Fig. 29. — Weather Map (fourth day). JiiUrOpean COUl WaVC 




52 PHYSICAL GEOGRAPHY. 

does not come from the northwest, where the Atlantic is 
tempered by the extension of the Gulf Stream, but from the 
continental area on the northeast. 

Weather predictions, as published by the Weather 
Bureau, are based on maps like those of the preceding 
figures, but much larger and more detailed ; observations 
for the maps are gathered by telegraph from all parts 
of the country. 

Under such conditions as those of Fig. 29, continued fair 
weather would be predicted for the Atlantic states, warmer 
weather with increasing cloudiness and rain for the Ohio 
valley and southern states, and clearing weather with lower 
temperature for the southwest. 

Climate. — The general succession of weather changes 
through the year, averaged for many years, constitutes the 
climate of a region. The five zones into which the earth 
is commonly divided need further subdivision in order to 
correspond to the many well-marked types of climate in 
different lands and seas. 

The trade-wind belt at sea has the simplest climate in the 
world, with small daily and yearly changes of temperature. 
The steady wind and fair weather of almost any day gives a 
fair example of the year. Lowlands under the regular trade 
winds suffer greater daily and yearly changes of temperature, 
with light rainfall. 

■ The subequatorial belt has distinct seasonal changes, as 
the clouds and rains of the heat equator move away and give 
place to the dry trade winds. On or near the geographic 
equator certain places have two wet and two dry seasons in a 
year ; for the heat equator crosses them twice, and between 
its visits they are occupied first by the northeast and then by 
the southeast trade winds. 



THE ATMOSPHERE. 53 

The subtropical belts have a distinct variation of tempera- 
ture between the warmer and colder parts of the year ; in 
summer they have the mild and regular climate of the trade 
winds ; in winter the more irregular and stormy climate of 
the westerly winds. 

The south temperate zone is mostly an oceanic belt. 
The changes of . air temperature with the seasons are 
small, because the water surface warms and cools so little 
in summer and winter. Its winds are more stormy in 
winter, less stormy in summer ; never very hot or extremely 
cold, but for the most part chill, damp, and blustering. 
Islands near 50° S. are hardly habitable, not that the 
winters are too severe, although cloudy and wet, but that 
the summers are too inclement. 

The north temperate zone contains large areas of land 
and water, and the climates of its various parts are there- 
fore very unlike. The parallel of 50° N. crosses regions 
whose climates are so different that they would hardly 
have been placed under a single zone had they been 
studied before being named. 

Beginning in the moderate climate of the Korth Atlantic, 
the parallel of 50° N. enters the favorable climate of middle 
Europe, where the last thousand years have witnessed the great- 
est human progress in the arts and sciences that the world 
has ever known. It crosses the broad deserts of central Asia, 
where the scattered population is held down in barbarism 
chiefly by severe and unfavorable climatic conditions. 

The broad North Pacific has a climate as moderate as that 
of the North Atlantic. Passing the tempered and moist cli- 
mate of the coast belt of British Columbia, and crossing the 
snowy mountain ranges beyond, the severe interior climate of 
middle Canada is reached, with extremes of temperature, sum- 



54 PHYSICAL GEOGRAPHY. 

mer and winter, only less than those of inner Asia. As far 
as habitability is concerned, the middle north temperate zone 
contains climatic differences almost as great as those found in 
passing from the equator to the pole. 

Relation of Climate and Vegetation. — The plants that 
so generally cover the surface of the lands grow by taking 
food from the air and the soil. Full-grown plants pro- 
duce seeds, most of which fail for one reason or another 
to grow ; but the others, germinating at a less or greater 
distance from their source, give rise to a new generation 
of plants, which produce seeds in their turn. In this way 
all kinds of plants might in time be distributed all over 
the world, if certain barriers did not oppose their progress. 

Young plants growing from heavy seeds, like nuts, slowly 
spread away from the parent plant. Plants growing from 
light seeds, especially from such as are carried by the wind, 
like those of the dandelion, the thistle, and the fireweed, are 
very rapidly diffused. 

Oceans and mountain ranges are the chief visible bar- 
riers to the diffusion of plants, but these are not so 
important as the invisible barriers of climate. Seeds 
might be carried by winds or birds across an arm of the 
sea or over a mountain range ; and if the climate is fitting 
at the end of their journey the seeds would grow and the 
plants would take possession of the new home offered 
them. But, however actively seeds are distributed, plants 
cannot invade a region whose climate is unfit for their 
growth. 

. Plants like palm trees, that flourish in the torrid zone, 
spread into lands in higher latitudes on both sides of the 
equator until they reach regions where the summers are too 



THE ATMOSPHERE. 55 

cool for their growth. Plants like corn and wheat, that 
occupy the temperate zones, are limited to belts on whose 
polar side the summer is too brief and cool, and on whose 
equatorial side the summer is too hot for their wider 
extension. 

Plants that need a plentiful rainfall cannot spread into 
those regions in which the winds fail to supply rain, even if 
the temperature is fitting. Thus corn, which grows so luxu- 
riantly in the Ohio, and middle Mississippi valleys, cannot be 
raised on the dry western plains without the aid of irrigation. 
On the other hand, many kinds of thorny cactus plants are 
found on the dry plains, but they cannot invade the moister 
regions further east. 

Relation of Climate and Animals. — Land animals, like 
plants, tend to spread over all parts of the earth to which 
they have access ; the limits of their distribution are con- 
trolled partly by climate and partly by food supply, which 
in turn depends on climate. Like plants, animals are 
limited on the polar side of their range chiefly by insuffi- 
cient heat in summer, and on the equatorial side by exces- 
sive heat in summer. Within the belt thus defined by 
the values of summer temperatures the distribution of ani- 
mals is largely controlled by food supply. 

Animals subsist either on animal or vegetable food ; but 
flesh-eating animals, like the lion, often devour plant-eating 
animals, like the antelope ; and thus in the end all animals 
depend for food directly or indirectly on plants, and the dis- 
tribution of plants has already been shown to depend on 
climate. 

The study of climate is therefore not only of importance 
in itself, but also from the control that it exerts over the 



56 PHYSICAL GEOGRAPHY. 

distribution of plants and animals, and thus indirectly 
over the distribution and occupations of mankind. 

Climate and Man. — Those parts of the torrid zone that 
have a moist climate support a luxuriant plant growth 
and contain a great variety of animals ; but they are not 
favorable to the development of the civilized races of 
man. In dry deserts and in the polar regions it is so 
difficult to gain a living that human progress is hindered. 
As a result of the generally small land areas of the south 
temperate zone the great ocean preserves a uniformly 
inclement climate, where man finds little opportunity 
for development. 

In those parts of the spacious north temperate lands, 
where the climate is neither too dry nor too severe, there 
is the great advantage of a winter that is cold enough to 
require the storage of food, and of a summer that is warm 
enough to provide the food to be stored. There can be 
little doubt that the habits of industry and thrift here 
made necessary, but not too difficult, have been of great 
importance in bringing civilization out of savagery. 



CHAPTER IV. 
THE OCEAN. 

The Exploration op the Ocean. 

Man's conquest of the ocean is one of his greatest 
triumphs. With wonderful daring and skill he has 
ventured to trust himself on the perilous waters. Un- 
dismayed by dangers and losses, he has persevered 




Fig. 30. — An Ocean Steamship. 



through centuries of effort, invention, and discovery, and 
now he travels almost as safely by sea as by land. He 
no longer relies upon the wind or oar to propel him, 
but with metal hull and tireless engines he defies the 
storms and uses the pathless ocean as a natural high- 
way in spite of its great perils. To-day the iron steam- 



58 PHYSICAL GEOGRAPHY. 

ship, a product of many highly developed arts, crosses the 
trackless seas so surely and quickly that the people of 
nations on the opposite sides of an ocean are coming to 
feel almost like neighbors. The length of a trip between 
the United States and Europe is so well timed that the 
date of arrival at its end is almost as regular as the date 
of sailing at its beginning. 

The thoughtful traveller reflects on the many lines of 
human progress that have led to the possibility of his voy- 
age. How little was it imagined when iron was first 
smelted from its ore, thousands of years ago, that the 
heavy metal would one day be used to build the safest 
kind of ships ! When the ancient Greeks watched the 
movements of the sun and stars, and studied the proper- 
ties of angles and circles, how little did they realize that 
from such beginnings the navigator would some day learn 
to guide himself across the broad seas ! Even as lately as 
when the steam engine was invented, little more than a 
century ago, no one supposed that steamships would so 
generally take the place of sailing vessels as they now do. 

Although a dweller on the lands, man has sailed over 
nearly all parts of the oceans. The narratives of exploring 
voyages, like that of Darwin's "Voyage around the World," 
present many volumes of entertaining and instructive read- 
ing. The shores of continents and islands have been care- 
fully surveyed and mapped. Soundings have been taken 
in the . shallower waters near the lands, to discover any 
hidden reefs that might endanger passing vessels. Sea 
captains on voyages in all parts of the world have faith- 
fully observed the direction and strength of the winds, so 
that advantage might be taken of them to shorten the 



THE OCEAN. 59 

voyages of sailing vessels. The currents of the ocean 
have been charted, so that they should not drift a vessel 
unawares out of its course. Tides have been measured at 
many ports, so that the time of high water may be calcu- 
lated in advance ; -the master of a vessel may now learn 
from his tide tables at what hour of any day he will find 
high water on approaching the shallow entrance of a har- 
bor. Even the depths of mid-ocean have been measured, 
and the bottom has been found a safe ground on which 
to lay submarine cables. As a result of this brave prog- 
ress, commerce has been greatly developed between distant 
parts of the world. 

The Physical Features of the Ocean. 

Form of the Ocean. — The ocean is a sheet of salt 
water, clear and blue, covering about three-quarters of 
the earth's surface to an average depth of about two miles. 
It lies in broad depressions between the continental masses, 
its shallow edges lapping over the land margins. 

A vast water area, comprising the Pacific and Antarctic 
oceans, covers nearly half the globe. Its surface is broken 
only by Australia, the Antarctic lands, and many small 
islands. A short Indian arm extends from this great 
oceanic area into the space between Africa and Australia ; 
and a long, relatively narrow Atlantic arm runs between 
the Old and New Worlds, ending in the gulf-like Arctic 
Ocean around the North Pole. 

The outline and distribution of the ocean should be studied 
on a globe. It may then be seen that the surface of a hemi- 
sphere whose pole is near New Zealand is nearly all water j 



60 



PHYSICAL GEOGRAPHY. 



while the opposite hemisphere contains all the large land 
areas, except Australia, the Antarctic lands, and the extremity 
of South America. It is not a little curious to note that near 
the pole of the land hemisphere stands the greatest city of 
the world, the capital of the empire whose colonies are more 
widely spread than those of any other nation. 

The Ocean as a Highway. — The lands are widely sepa- 
rated by the oceans, and navigation of the " high seas " 



^^jsaj^ssj^^ 



^-^^^* 




Fig. 31. — Land and Water Hemispheres. 

requires great skill and is fraught with many dangers. 
But the oceans are a ready-made highway, where move- 
ment is easy and open to all comers, and the winds furnish 
free motive power to sailing vessels. Hence transportation 
in ocean-going vessels is very economical. Before rail- 
roads were invented, the two sides of the North Atlantic 
were in more active communication by sea than the two 
sides of any continent overland. Since railroads have 
been extensively built, inland transportation has greatly 
increased; but a great part of international commerce is 
still carried on across the oceans. 



THE OCEAN. 



61 



Exploration of the Ocean. — The earlier exploration of 
the ocean discovered its continental shore lines and its 
islands. Exploration in the latter part of the nineteenth 
century has penetrated its depths and reached its bottom. 

Soundings are now made with much accuracy, even to depths 
of four miles or more. Fine steel wire is used for a line ; the 
sinker is a heavy iron ball that is automatically detached 





Fig. 32. — Sounding Instrument and Water 
Bottle. 



Fig. 33. — Deep-Sea Thermometers. 



on touching the bottom ; then the wire is rapidly reeled in 
by steam power. A sounding of 3000 fathoms (one fathom 
equals six feet) can be completed in about an hour. 

The temperature of the deep water is taken by self-regis- 
tering thermometers. They must be protected by an outer 
glass tube against the tremendous pressure of the deep water. 
Samples of water are obtained from various depths by the use 
of brass tubes, called " water bottles," sent down open, but 
automatically closed when reeling in begins. 



62 



PHYSICAL GEOGRAPHY. 



Specimens of the ocean bottom are gathered by dredges ; 

wire rope is needed to haul up the ton or more of material 

that they take in while dragged on the sea floor at depths 

of one, two, or even three miles. Nets are sometimes attached 

to the rope for the chance of catching 

I animals at different depths. The best 

nets are closed while sinking and rising, 

being opened only while trolling at the 

greatest depth that they reach. 



'1 



T 



Fig. 34. — Dredge. 



Ocean Depths. — Soundings have 
shown that the ocean basins are com- 
paratively steep-sided and flat-floored. 
The greatest depth yet found is 5155 
fathoms (30,930 feet) in the South 
Pacific, near the Fiji Islands. Another 
place of great depth in the Pacific, 
over 4600 fathoms, lies northeast of 
Japan. 

The deepest sounding yet made in 
the Atlantic is 4561 fathoms, in a local depression about 
100 miles north of Puerto Rico, West Indies. The 
Atlantic is generally less deep along its middle (1500 
to 2000 fathoms) than on either side (2500 to 3000 
fathoms), the shallower middle part being sometimes 
called a " ridge " or " swell." 

Composition and Density. — The mineral substances dis- 
solved in ocean water constitute about three per cent of 
its weight ; their presence makes it heavier than pure water 
in the proportion of 1.026 to 1.000. Although water is 
easily moved, it is very little reduced in volume even 
when compressed by great forces. Hence, in spite of the 



THE OCEAN. 63 

great pressure of the upper layers of the ocean on those 
beneath, the ocean is of nearly uniform density from top 
to bottom. Anything that is heavy enough to sink at the 
top will sink all the way to the bottom. 

The ocean contains a great variety of substances in solu- 
tion, for it has received everything that streams have dis- 
solved and carried from the lands for ages past. Common 
salt makes three-quarters of the dissolved substances. An 
important but much less plentiful dissolved substance is 
limestone, of which many sea animals make their shells or 
skeletons. 

A small quantity of atmospheric gases is found dissolved 
in sea water, even in its deepest parts. It is upon the oxygen 
thus supplied that fish and most other marine animals depend 
for " breathing " ; but whales and other mammals living in the 
ocean come to the surface for air. 

Ocean Temperatures. — ■ The surface layers of the ocean 
vary in temperature with latitude, reaching about 80° 
around the equator, and being reduced to 30° or 28° in 
the polar regions. The great body of the deep ocean is 
cold in all latitudes ; its temperature is about 30° in high 
latitudes and 35° or 40° in the torrid zone. 

When exploring vessels dredge in torrid oceans, the sedi- 
ments brought up from the bottom have a temperature near 
freezing, strangely in contrast with that of the objects on 
shipboard under a hot sun. 

The sun's rays have small effect on ocean water at depths 
below 100 or 150 fathoms. At greater depths the ocean 
must be nearly dark, with hardly perceptible difference 
between day and night, or between winter and summer. 



64 



PHYSICAL GEOGRAPHY. 



The temperature at any point in the great body of the 
deep ocean is nearly constant. 

In Fig. 35 depth is measured downward, and temperature 
horizontally. Curve ABC shows the change of temperature 

with depth in the torrid 



30 (? 



500 
H 



1000 



1500 



J 

2000; 



TEMPERATURE t^ttttjt • .i . 

40 50 D 60 70 jg^ 80 occans ; DUF, m the tem- 

^/ ^.iy perate oceans ; and GHJiu 

^.""^ .--":.'^ the frigid oceans. Below 400 fath- 

/ y' 4 oms the curves are all much alike. 



El 



M\ 



F 



The daily and annual range of tempera- 
ture in the ocean surface is very small, 
seldom more than 3° and 15°, respectively. 
As the temperature of the lower air is 
largely controlled by that of the surface 
on which it rests, the climate of mid-ocean 
islands and of continental borders where 
the prevailing winds blow ashore is free 
from great changes of temperature between 
winter and summer. 

Salt water contracts and increases in 
density down to its freezing point, 28°. 
Hence the cooled surface water of high 
latitudes sinks to great depths and creeps 
very slowly towards the equator ; thus the low tempera- 
ture of the great body of the ocean is accounted for. 

A movement in the deep waters is also proved by the pres- 
ence of dissolved oxygen in specimens of water brought up in 
" water bottles " from great depths. The oxygen is gained 
from the atmosphere, and as the animals of the deep sea 
use it in ''breathing," the supply would long ago have been 
exhausted had it not been renewed. (See Appendix K.) 



Fig. 35. — Curves 

of Ocean 

Temperatures. 



THE OCEAN. 



65 



Fresh water is unlike salt water in being densest at 39°. 
On being warmed or cooled from this temperature it expands 
and becomes lighter.' Hence in winter, when all the water 
of a lake has been cooled to 39°, further cooling affects only 
the surface water, which then soon freezes. 

Ice -in the Ocean. — The ice formed from salt water 
expands a little as it freezes, and therefore floats. The ice 




rig. 36. — A Vessel teset by Pack Ice. 

thus formed in the polar oceans is known as floe ice; it 
may reach a thickness of from 3 to 7 feet in a single 
winter. 

Great fields of floe ice drift with the winds and currents. 
They may thus be torn apart or crushed together. When 
two floes collide, pack ice of very irregular surface is formed ; 
it may reach a thickness of over 100 feet. 

In the return of Greely's expedition to the Arctic regions 
in 1883, his boats were frequently in danger of being crushed 



66 



PHYSICAL GEOGRAPHY. 



when ice fields drifted together, closing the water passage he 
had been following. 

Smooth floe ice is easily crossed on sleds. The Eskimos 
make winter journeys upon it. Where packed, it may be im- 
passable. It was on account of the roughness of ridged pack 
ice that Nansen had to turn back from his " dash for the pole," 
in latitude 86° 13' N., longitude 96° E., on April 8, 1895. 




Fig. 37. —An Icetierg. 

When two large fields of pack ice drift together, a vessel 
between them would be crushed, unless of great strength, 
and shaped so as to escape by rising. Nansen's vessel, the 
" Fram," was especially constructed to withstand great pres- 
sure, and so survived the dangers to which it was exposed. 

Icebergs in the North Atlantic are fragments of glaciers 
formed on Arctic lands, chiefly Greenland; they are of 
fresh water. The tabular icebergs of the Antarctic Ocean 
are fragments of a heavy sheet of ice that is believed, to 
rest upon land or upon a shallow ocean bottom around the 



THE OCEAN. 67 

south pole. Some of these ice blocks measure a mile or 
more on a side, and 1200 to 1500 feet in thickness. The 
height of icebergs above the sea is about one-sixth or one- 
seventh of their depth below the surface. 

Collision with an iceberg is one of the dreaded dangers of 
navigation in high latitudes. In the southern oceans drifting 
icebergs reach latitude 60°, or. even 40°. In the North Atlan- 
tic they reach latitude 45° southeast of Newfoundland, but 
they are absent from the northwestern coast of Europe even in 
latitude 70°, on account of the warm water there prevailing. 
They are wanting in the North Pacific, except in the bays of 
the Alaskan coast. 

The Ocean Bottom, — '■ The greater part of the deep ocean 
bottom is a comparatively even plain of soft ooze ^ of simi- 
lar composition and form over great areas. The plain rises 
and falls gently in broad swells, but is not varied by hills 
and valleys of uneven form. Its smoothness is due to the 
slow but long-continued gain of material chiefly from the 
surface and in small part from the margins. 

No mountain ranges with sharp peaks and ridges separated 
by deep passes and valleys have yet Iseen discovered on the 
open ocean floor far from the continents. But Cuba and some 
of the neighboring islands in the West Indies seem to be the 
crests of a mountain range, whose western extension forms 
submarine ridges in the northern Caribbean, dividing it into 
a number of deep basins, and connecting the islands with 
Central America.- 

Volcanic and coral islands are the most abrupt forms of the 
deep ocean. Volcanic cones sometimes rise above the ocean 
surface, forming lofty mountains, as in the Hawaiian Islands ; 
sometimes they are known only by soundings. 

1 rine-textured deep-sea deposits of animal origin are called ooze ; if 
derived from the wash of the lands, they are called muds. 



68 PHYSICAL GEOGRAPHY. 

The calcareous (limy) ooze which covers a large part of 
the ocean floor consists of the minnte shells, more or less 
decayed, of simple animal forms that live at or near the sur-, 
face. One of these, highly magnified, is shown in Fig. 38. 
In greater depths than 3000 fathoms the ooze is commonly 
replaced by a reddish clay, which is believed to be a very 




Fig. 38. — Globigerina (magnified 100 times). 

slowly accumulating deposit of insoluble substances that 
remain after the calcareous material of the minute shells is 
dissolved in the deep-sea water. 

*' The monotony, dreariness, and desolation of the deeper 
parts of this submarine scenery can scarcely be realized. The 
most barren terrestrial districts must seem diversified when 
compared with the vast expanse of ooze which covers the 
deeper parts of the ocean," 



THE OCEAN. 



69 



Mediterraneans. — .Besides the open oceans thus far con- 
sidered, there are several deep seas, more or less separated 
from the oceans by land barriers. The most important of 
these is the classic Mediterranean (the sea " in the middle 
of the lands "), averaging nearly as deep as the great 
oceans, but connected with the Atlantic only by the 
narrow and shallow strait of Gibraltar. 

Other similar mediterranean seas are the Caribbean and 
the Mexican (deep central part of the Gulf of Mexico). 
The former has many inlets from the Atlantic between 
the various islands of its eastern rim ; it is divided into 



CARIBBEAN SEA 

70-80^ 



ATLANTIC OCEAN 

70-80° 




Fig. 39. — Temperatures of the Caribtean Sea. 

several deep compartments by ranges of the West Indian 
submarine mountain range. The latter is a single basin. 

Several mediterraneans of moderate size are found east of 
Asia. The Japan, China, Sulu, Banda, and Celebes seas are 
the most important ; they are imperfectly enclosed from the 
Pacific by island chains. 

The deep water of mediterraneans is warmer than that of 
the adjacent oceans, as shown in Fig. 35, KLM. The tem- 
perature of the Caribbean Sea is 39^° at great depths, as in 
Fig. 39, this being the temperature of the adjacent Atlantic at 
the depth from which the water in the Caribbean is supplied ; 
for the deepest connecting channel, east of Puerto Eico, has a 
temperature of 39-g-° at its bottom, 900 fathoms. The deep 
Atlantic is several degrees colder. 

The Mediterranean has a constant temperature of 55° from 
a depth of about 250 fathoms to the bottom (over 2000 



70 



PHYSICAL GEOGEAPHY. 



fathoms), this being somewhat colder than the adjacent 
Atlantic at the depth of the shallow entrance near the strait 
of Gibraltar.^ In winter the northern Mediterranean is of 
uniform temperature from toj) to bottom ; hence it is believed 
that this sea repeats the condition of the oceans in accumu- 
lating in its greatest depths the coldest water that is supplied 
at the surface. 

Continental Shelves. — The ocean often overlaps the 
borders of the continental masses in a comparatively shal- 
low belt of water, at whose outer edge the depth is com- 



Continent 



ts Shallow Water on 

<<? Continental Shelf 



Deep Water 




Fig. 40. — Section of Continental Shelf. 

monly about 100 fathoms ; thence it rapidly sinks to the 
deep ocean floor. These shallow bottoms are known as 
continental shelves. The water on the shelf is often 
greenish from fine suspended sediment, unlike the clear 
deep blue water of the open ocean and the yellowish water 
opposite the mouths of great rivers, such as the Amazon 
and the Hoangho. 

The gravel, sand, and clay washed from the lands are 
more or less moved about by waves, currents, and tides on 
the continental shelves. Thus they are slowly ground 
finer and finer, and their finest particles are gradually 
moved outward to deeper water. They are seldom found 

1 The water in tlie strait is over 400 fathoms deep ; a less depth is 
found a short distance westward. 



TSE OCEAN. ■ 71 

in dredgings over 200 miles from shore ; for the most part 
they are carried a less distance. In the course of ages the 
sediments thus accumulating may form successive layers 
or strata hundreds of feet thick, including many shells and 
other relics of marine life. 

The lowland borders of continents are often built of layers 
of sand and clay frequently containing marine fossils ; thus 
suggesting that a former sea bottom has there been raised to 
a land surface. 

A well-defined continental shelf, from 50 to 100 or more 
miles in width, stretches along the eastern side of North 
America from JSTewfoundland to Florida, and thence around 
the Gulf of Mexico. The British Isles stand upon a conti- 
nental shelf that borders mid-western Europe. The Malayan 
and Australian islands surmount broad shelves between Asia 
and Australia, separated by a belt of deeper water. 

Continental shelves are of great importance as the chief 
fishing grounds of the world. The European ports around 
the. North Sea send out hundreds of fishing vessels to its 
shallow waters. The rich fishing grounds of the New- 
foundland Banks attracted many fishermen from the Old 
World over three centuries ago. 

Waves. - — When the wind blows over the sea, the water 
gains an undulating motion, forming waves that advance 
with the movement of the wind. Although the wave form 
moves forward, the water only oscillates up and down, 
back and forth, without progressive motion. The stronger 
the wind, the higher the crests and the lower the troughs 
of the waves ; and the greater their length or distance from 
crest to crest, the deeper their disturbance extends beneath 
the surface, and the faster their progressive motion. 



72 



PHYSICAL GEOGRAPHY. 



Great waves formed in the open ocean by gales and 
hurricanes are often called seas. Their height from 
trough to crest reaches 30 or 40, but seldom exceeds 50 
feet. Their length varies from 300 to 1500 feet or 
more, and their velocity from 20 to 60 miles an hour. 
The interval between the passage of successive crests, or 
the period of the wave, is seldom more than 10 seconds. 




Fig. 41. — Orbital Movement of Water in Waves. 

The water particles in waves move forward in the crest 
(Fig. 41), downward on the back, backward in the trough, 
and upward in the front of the next wave. Hence each 
particle moves around a curved path every time that a 
wave passes by ; the movement of the wave being con- 
stantly in one direction, wliile the water particles rise and 
fall, advance and retreat, at a much less speed. 



The waving of a field of grain under the wind may be taken 
as an illustration to show the relation of the curved-path 
movement of the particles to the forward progress of the 



THE OCEAN. 73 

waves. The independence of wave and water movement may 
be seen on a river surface when the wind is blowing up stream"; 
or at the mouth of a harbor when the wind is blowing on shore 
while the tide is running out. 

It is fortunate that only the shape of great waves has a 
rapid forward movement, while the water oscillates at a mod- 
erate rate. If the water moved forward with the waves, ves- 
sels would be swept thousands of miles from their courses and 
thrown violently on the shores ; the ocean would not be 
navigable. 

In the construction of ocean steamers and war vessels 
it is important that the period in which they naturally 
roll (like the period of a swinging pendulum) shall be 
longer than that of any waves they are likely to meet; 
for if the two periods agreed, the repeated action of the 
waves might make the vessel roll more and more until it 
capsized. 

A small quantity of oil poured on the sea spreads 
rapidly and reduces the violence of the waves in a storm. 
A gale ordinarily forms ripples and small waves on the 
backs of greater waves, and causes the crests of great seas 
to curl over, so that they would break with destructive 
strength on the deck of a vessel. At such a time a film 
of oil decreases the catch of the wind on the water and 
prevents the large waves from curling and breaking. 

Many accounts of the use of oil in storms have been pub- 
lished by the United States Hydrographic Office, Washing- 
ton. They show that, when a vessel is headed towards the 
wind (" hove to ") and heavy seas come on board over the 
bow, a little oil allowed to drip from a bag will spread even 
towards the wind, forming a smooth surface or <' slick"; and 
the waves entering the slick will decrease in height and cease 
breaking over the deck. 



74 PHYSICAL GEOGRAPHY. 

When a vessel is running with, the wind, iieavy seas some- 
times come aboard over the stern ; but if a little oil is allowed 
to drip overboard, the slick spreads out like a fan across the 
wake, and the great seas are roimded off as they run into it, 
so that the vessel rides them without difficulty. 

Great waves, travelling 20 to 60 miles an hour, soon 
run out of the storm that forms them and swing far 
across the ocean, preserving their length and velocity, but 
diminishing in height. In this reduced form a wave is 
called a swell. 

In calm weather the ocean surface may be smooth and 
glassy, but not absolutely level and quiet ; for it is never free 
from the slow heaving and sinking of fading swells from 
distant storms. A vessel becalmed in the doldrums always 
swings idly to and fro as the swell rolls by. 

When the swell runs into shoaling water near land, its 
velocity decreases ; its crest rises, and its trough sinks, 
thus making its height greater ; the front becomes steeper 
than the back ; and on reaching a sloping shore the crest 
curls forward and dashes upon the beach, forming surf or 
breakers. 

The surf is like a mill in which rocks, gravel, and sand on 
the shore are ground finer and finer. During storms surf 
exerts an enormous force capable of moving blocks of rock 
10 or more feet in diameter. 

Exposed coasts may be beaten by a heavy surf while 
the neighboring sea is unruffled by the wind. The surf 
is then derived from a broad swell, which comes from the 
great waves of a storm that may be 1000 or more miles 
away. 



THE OCEAN. 



75 



The great hurricane -of Sept. 3-12, 1889, while on its way 
from the West Indies to the Carolina coast, produced a 
destructive surf on the coast of ISTew Jersey while the storm 
area was still a thousand miles distant. At St. Helena, a 
lonesome island in the South Atlantic, boats from vessels at 
anchor in the harbor frequently cannot reach the shore in 




Fig. 42. — Surf. 



fair weather on account of the " rollers," or heavy surf, on the 
beach. The swell that produces this surf is believed to come 
from storms in temperate latitudes of the North Atlantic. 



Earthquake Waves. — When an earthquake, caused by 
some disturbance in the earth's crust, occurs beneath the 
sea, the whole body of the ocean above it is moved 
slightly, -and the movement then spreads away on all 
sides in long, low waves that travel with great speed. 
When nearing the shore, the speed and length of the 



76 PHYSICAL GEOGEAPRY. 

wave are decreased, but the height is greatly increased. 
The wave may then rush far in on a lowland coast, caus- 
ing great destruction. 

The tremendous explosive eruption on the volcanic island 
Krakatoa, between Java and Sumatra, in August, 1883, pro- 
duced waves that spread far around the world. Their aver- 
age velocity of progression was nearly 400 miles an hour. 
On distant coasts their rise and fall was slight ; but on coasts 
near Krakatoa the waves rushed upon the land with a height 
of from 50 to 80 feet, flooding the lowlands, sweeping away 
many villages, and drowning thousands of the inhabitants. 
A large vessel was carried a mile and a half inland and 
stranded 30 feet above sea level. 

An earthquake in the North Pacific produced a destructive 
wave, 10 to 50 or more feet high, on the coast of northern 
Japan in the evening of June 15, 1896. The coast was laid 
waste for 175 miles. The few persons who saw the wave and 
survived it reported that the sea first drew back about a 
quarter of a mile, and then came rushing in like a black wall, 
gleaming with phosphorescent light and overwhelming the 
shore. On the open coast the sea became quiet in a few 
minutes after the wave broke ; but in bays the water surged 
and swirled for half an hour. The outline of the shore was 
changed in many places ; many villages were destroyed, and 
thousands of acres of arable land were laid waste. Thousands 
of fishing boats were crushed or carried away ; 27,000 persons 
lost their lives, and 60,000 survivors were left homeless. 

It is thought that earthquake waves are sometimes pro- 
duced, by great masses of fine sediments sliding down the 
slopes of continental shelves. In Japan many earthquakes 
are ascribed to this cause. Telegraph cables lying on such 
slopes are especially subject to injury ; when raised for re- 
pairs, they are found torn, as if violently dragged with the 
slidinar sediments. 



THE OCEAN. 



77 



Ocean Currents. — The upper waters of the ocean, to a 
depth of 50 or 100 fathoms, move slowly in the general 
direction of the prevalent winds, thus forming currents 
that circulate about the great oceanic areas. The outline 
diagram of ocean currents (Fig. 43) shows that each of 




Fij. 43. — Chaxt of Ocean Currents. 



the great oceans possesses a great eddy-like current that 
moves slowly around it, leaving the central waters rela- 
tively quiet. 

If an observer stood in the center of an oceanic eddy in 
the northern hemisphere, the currents would pass around him 
from left to right ; in the southern hemisphere, from right to 
left. 

The eddying currents are the chief natural basis for sub- 
dividing the great oceanic area into the six oceans ; the North 
and South Pacific, the North and South Atlantic, and the 
Indian oceans, each has its own great eddy ; while the 
Antarctic Ocean has a great eddy around the south pole, 
joining the eddies of the three southern oceans. The Arctic 
also has a current about the pole, joining that of the North 



78 



PHYSICAL GEOGRAPHY. 



Atlantic, somewhat like the two loops of a figure 8 ; but the 
Arctic should be classified as a large sea or gulf, rather than 
as an ocean. 

A current that advances slowly in a broad and shallow 
sheet at a rate of 10 or 15 miles a day, like that which 

crosses the middle North 
Atlantic, shouldbe called 
a drift. A current that 
flows rapidly in a com- 
paratively narrow pas- 
sage, with a velocity of 
50 or more miles a day, 
like that issuing from 
the Gulf of Mexico 
strait of Florida, should be called a stream. 




Fig. 44. 



- Displacement of a Vessel by 
Currents. 



^Wi^ 



through th€ 

It is important that the masters of vessels should be ac- 
quainted with the movements of ocean currents. In cloudy 
and foggy weather, 
when observations of 
the sun cannot be 
made to determine lati- 
tude and longitude, a 
vessel might be drifted 
out of its expected 
course if no allowance 
were made for the 
movement o*f the 
waters. Thus if, in- 
tending to follow the 
course MahcN (Fig. 
44), a vessel were 
drifted to the course 
MABCB, it would pass dangerously near the headlands at B 




Fig. 45. — Drift of floating Objects by 
Currents. 



THE OCEAN. 79 

and C, and might even run ashore. Wrecks on the southwest 
coast of Ireland have not infrequently been due to this cause. 

The drift of abandoned wrecks, whose positions are noted 
by passing vessels, gives indications of the movements of cur- 
rents. The angular lines in Fig. 45 show the drift of several 
wrecks. The broken lines indicate the drift of many logs 
from a great timber raft that was abandoned in a storm while 
on the w-ay from the Canadian Provinces to New York, Decem- 
ber, 1887. 

Thousands of bottles have been thrown into the sea, with 
record of the time and place where they have been set adrift, 
and request that the finder shall report the time and place of 
their discovery, afloat or ashore. The dotted lines of Fig. 45 
give a few inferred " bottle tracks." 

In Hansen's famous attempt to reach the north pole he 
sailed eastward along the northern coast of Asia and turned 
northward into a region of ice fields, where his vessel was 
caught between two floes. He then drifted with the ice, 
expecting that the Arctic current would carry him past the 
pole towards Greenland. Had he gone further east before 
turning north, a closer approach to the pole might have been 
made. 

The remarkable correspondence between the course of 
the oceanic eddies (Fig. 43) and the course of the prevail- 
ing winds over the oceans, as shown in the charts, Figs. 
19 and 20, points to the winds as the cause of the cur- 
rents. Like the circulation of the atmosphere, the eddy- 
ing of the upper waters of the oceans must be regarded as 
a characteristic habit of a globe having large oceans, a 
mobile atmosphere, and a warm equatorial zone. 

The belief that the winds cause the currents is confirmed 
by the way in which the surface drift of the waters may be 
for a time brushed to one side of its usual course, or even 
reversed, during a storm. 



80 



PHYSICAL GEOGRAPHY. 




Fig. 46. 



■ Currents of the Indian Ocean 
in July. 



The currents of the Indian Ocean, with its gulfs on the 
north of the equator, show an extraordinary variation in 

direction, following the 
change in the blowing of 
the monsoons. During 
the northern summer, 
when the southwest mon- 
soon is developed north 
of the equator (Fig. 23), 
the waters under it have 
a general eastward mo- 
tion, as in Fig. 46. Dur- 
ing the southern summer, 
when the northwest mon- 
soon is developed south 
of the equator (Fig. 24), 
the waters under it also 
move eastward, while on 
the north of the equator the currents run in a general westerly 
direction under the north- 
east monsoon of that re- 
gion, as in Fig. 47. 

East-flowing currents of 
this kind near the equator 
are called counter cur- 
rents, because they move 
in a direction opposite to 
that of the equatorial 
members of the great 
eddies. 



The several parts of 
the various eddies may 
receive special names. 
Those parts which run 
westward, near and about parallel to the equator, are called 




Fig. 47. — Currents of the Indian Ocean 
' in January. 



TRE OCEAN. 81 

the equatorial currents. The eastern part of the South 
Pacific eddy is called the Humboldt, or Peruvian, current; 
it brings a great body of cool water from far southern lati- 
tudes, and keeps the temperature about the Galapagos 
Islands (west of Peru) so low that coral reefs, such as 
abound in the equatorial Pacific further west, are not 
found on their shores. 

The name Gulf Stream, in the Atlantic, should be 
properly limited to the narrow, deep, and rapid current 
issuing from the Gulf of Mexico, where its velocity reaches 
80 or 90 miles a day; but it is popularly extended far 
northeast over the broad, shallow, and slow-moving drift 
on the northern side of the North Atlantic eddy, and even 
along its branch, past Norway. This extension of the 
current is not a stream at all, and it includes much water 
that passed outside of the West Indies and not through 
the Gulf of Mexico. 

Sailing vessels should take advantage of winds and cur- 
rents in shaping their courses. If bound from the United 
States to far South American ports, they should cross the 
equator well to the eastward, so as to avoid being carried 
backward by a strong current past the Guiana coast, where 
the winds may fail in the doldrums. A ship sailing from an 
Atlantic port to Australia should round Cape of Good Hope 
and take advantage of favorable winds and currents in the 
southern Indian Ocean about latitude 50°. On the homeward 
voyage favoring winds and currents would be found in the 
same latitude of the South Pacific, towards Cape Horn. 

Currents and Temperatures. — Certain ocean currents 
carry warm water poleward; others carry cold water 
equatorward, thus causing an irregular arrangement of 
sea-surface temperatures. The eddying winds over the 



82 



PHYSICAL GEOGBAPHT. 



several oceans and the bordering continents cause similar 
irregularities in atmospheric temperatures. In a general 
way the eddying of the waters and winds narrows the 
warm belts on the eastern side of the torrid oceans, and 
widens the temperate belts on the eastern side of the 
oceans in middle latitudes. 

The effect of currents and winds in disturbing the even 
arrangement of temperatures is much less distinct in the 
southern hemisphere, where only one continent extends over 
50° from the equator, than in the northern hemisphere, where 
the continents almost enclose the polar sides of the oceans. 
The eastern drift of the far southern surface waters (forming 
the Antarctic circum polar eddy) is little interrupted, and 
the temperature belts follow close along the parallels of 
latitude. 

The temperature belts of the North Atlantic are more 
disarranged than those of any other ocean. This is because 
of the shape of its shores. It gains 
a large branch current from the 
South Atlantic, thus giving it an 
undue amount of warm water in the 
neighborhood of the West Indies; 
a great branch of its eastward drift 
turns northeast, past the British 
Isles and Norway; and a cold cur- 
rent, returning from the Arctic 
regions, flows past Labrador and 
Newfoundland. The belt of tem- 
perate climate (Fig. 48) is broadly 
spread over the western coast of 
the Old World between latitudes 30° and 60°. The same 




Fig. 48. 



Temperatures on the 
Atlantic. 



THE OCEAN. 



83 



climatic belt is compressed between latitudes 30° and 45° 
on the eastern coast of North America. 

Florida and Nova Scotia differ as much in mean annual 
temperature as Morocco and Norway. Labrador is a bleak, 
desolate region very thinly inhabited, while England, in the 
same latitude on the opposite side of the Atlantic, has a mild 
climate and a dense population. The chilling northeast wind 
of New England is part of a cyclonic whirl, supplied by air 
that has been lying over the cold Labrador current. 

Tides. — Regular movements of the ocean, rising and 
falling on the shores twice in a little more than a day, 
are called tides. In the open ocean tides are not per- 
ceived ; in many bays the tidal change of level, or range, 








Fig. 49. — High Tide, 

reaches 10, 20, or more feet. The change of level is 
accompanied by currents — flood tide running in from the 
open ocean, ebb tide running out again. A brief period 
of quiet or slack water occurs when flood changes to ebb, 
or ebb to flood. 



84 



PHYSICAL GEOGRAPHY. 




Fig. 50. — Low Tide. 

The following table and diagram (Fig. 51) give the time 
of high and low water and the direction and velocity of flood 
and ebb currents for several stations in a large bay, which lead 
to a number of important conclusions. 

The interval or period between the times of successive high 
tides is constant at all stations, being 12 hours 26 minutes. 

The range of the tide increases from the entrance towards 
the head of the bay, and then diminishes up the tidal river or 
estuary further inland. 

The rise and fall are of equal duration at outlying stations, 
low tide occurring at mid-interval between high tides ; but 
near the head of the bay the rise is more rapid than the fall, 



Sta- 
tion. 


2 S 


Rise. 


Cur- 
rent. 




O H 


Fall. 


Cur- 
rent. 




li 


Rise. 




li.m. 






h.m. 


h.m. 






h.m. 


h.m. 




A 


0.05 


2 ft. 


Im. 


3.10 


6.20 


2 ft. 


Im. 


9.25 


12.30 


2 ft. 


B 


2.10 


3 


2 


5.15 


8.25 


3 


2 


11.25 


14.35 


3 


C 


2.55 


3 


2 


6.10 


9.10 


3 


2 


12.20 


15.20 


3 


D 


4.25 


4 


2 


8.05 


11.50 


4 


2 


14.20 


16.50 


4 


E 


8.30 


5 


3 


12.35 


16.40 


5 


3 


18.50 


20.55 


5 


F 


15.05 


6 


3 


19.30 


0.00 


6 


3 


1.45 


3.30 


6 


G 


22.20 


6 


3 


3.10 


7.55 


6 


3 


9.20 


10.45 


6 


J 


4.00 


4 


2 


8.20 


12.45 


4 


2 


14.35 


16.25 


4 



THE OCEAN. 



85 



and low tide occurs nearer the following than the preceding 
high tide. 

Dotted lines are drawn in Pig. 51 to indicate the inferred 
position of high tide in the bay at the even hours. The 
advance of high tide is then seen to be about 50 miles an hour 
in the deeper water off-shore, but only 10 miles or less in the 
shallow water near the bay head. 

The flood and ebb currents run past the outlying stations 
(A, B) for some time before and after high water. At the 
head of a little bay, like L, slack water occurs at high and 
low tide ; flood currents run while the tide rises, and ebb 
currents while it falls. 




Fig. 51. 



- Diagram showing FrogTessioii of High 
Tide up a Bay. 



When high water occurs in the entrance to the bay, the 
high waters of two preceding tides are near the head of the 
bay, as shown in section in Fig. 52. Many actual examples 
illustrating these phenomena may be found in the Charts and 
the Tide Tables published by the U. S. Coast Survey. 



Birjh 


Bioh 


D 


c 


B 


A nigh 


^si. si^ 


\^f5/^tacfc Mean siaclc'-^ 
Ebb 


^ Loio 





-" Slack 






'Ebb 







Fig. 52. — Diagram of Tide Waves. 



86 PHYSICAL GEOGRAPHY. 

It appears from the foregoing that tides resemble waves 
in many ways. High tide is the crest of the long, flat 
tidal wave ; low tide is the trough. Tidal currents cor- 
respond to the curved-path movements of water in ordinary 
waves. The change in the range, velocity, and form of 
the tide, as it advances up a bay, may be compared to the 
change in the behavior of the ocean swell as it runs ashore. 

Cause of the Tides. — The regular arrival of wave-like 
tides on all ocean shores leads to the belief that the whole 
ocean must be undulating. The tide waves in the open 
ocean must have a less range and a greater velocity than 
the tide waves near shore ; but the period must everywhere 
be 12 hours 26 minutes. The undulation of the oceans 
must be caused by some disturbing force that acts in the 
same period as that of the tides. 

The apparent daily movement of the moon carries it 
from one side of the earth to an opposite position in 12 
hours 26 minutes ; and this fact suggests that the moon is 
the cause of the tides. The power of the moon to produce 
the tides can be reasonably explained as a result of the 
attraction that it exerts on the earth and the oceans. 

It was known to the ancient inhabitants of Great Britain 
in the time of Julius Csesar, almost 2000 years ago, that 
there was some relation between the moon and the tides ; but 
Newton, the great English mathematician and astronomer, 
first gave about two centuries ago a clear explanation of 
the process by which the moon can produce tides. (See 
Appendix J.) 

Tides are beneficial in maintaining a circulation in bays 
and harbors where the waters might otherwise be almost 



THE OCEAN. 



87 



stagnant. At high water a harbor will admit vessels of a 
larger size than could enter if the ocean level did not 
change ; but at low water the harbor may be inaccessible 
except to much smaller vessels. 

In funnel-shaped bays or estuaries the tidal range becomes 
large, and flood and ebb currents are very strong, making 
navigation difficult or even dangerous. The tidal range 




Fig. 53. — The Tidal Wave or Bore in the Seine. 



sometimes exceeds 50 feet at the head of the Bay of Fuudy 
and of the Bristol channel ; here the flood current rushes in 
like foaming surf. The estuary of the Seine in France has 
a similar surf-like tide, shown in Fig. 53. Such surf-like 
tides are called bores. 

Many curious tidal phenomena are found on shore lines of 
different forms. At New York a high tide entering from the 
harbor reaches the rocky narrows of Hell Gate when a low 
tide arrives through Long Island sound; and six hours later 
a low tide from the harbor meets a high tide from the sound. 
Thus a rapid current is caused to flow back and forth in the 
narrow passage, which was dangerous to vessels until the 
channel was widened by blasting away its reefs. A current 
of this kind is sometimes called a tidal race. 



88 PHYSICAL GEOGRAPHY. 

Faint tides are observable in large lakes. In Lake Michi- 
gan at Chicago, and in Lake Superior at Duluth, the strongest 
tides have a range of about three inches, but they are usually 
marked by an irregular rise and fall of the water due to 
on-shore and off-shore winds. 

Life in the Ocean. — The surface layers of the open 
ocean possess a considerable variety of animal life, from 

large mammals like 
whales to minute or- 
ganisms (Fig. 38) whose 
tiny shells are so plenti- 
fully strewn over the 
ocean floor. The former 
occur in moderate num- 
bers; the latter are 
countless. The distri- 
bution of surface life is 
determined chiefly by 
differences of tempera- 
ture from the torrid to 
the frigid zones. Those 
forms which swim or are 
drifted freely by the 
currents are found over 
vast areas. 

In fair weather the surface waters are sometimes alive with 
minute, jelly-like forms. In the warmer seas the phosphores- 
cent light which these simple organisms produce wheu dis- 
turbed, as in rippling waves or in the wake of a vessel, makes 
the water glow at night. 

The relatively quiet water about the central part of the 
great surface eddies generally contains a considerable quan- 




Fig. 54. — A Floating Jellsrfish. 



THE OCEAN. 



89 



tity of. floating seaweed, or sargassuvi ; hence these central 
areas are called sargasso seas. The sargasstcm is believed to 
be derived from shallow marginal waters, where it grows on 




Fig. 55. — Deep-Sea Fish, x J. 

the bottom. A great variety of small animals live on the 
floating weed, and a certain kind of fish uses it as a " nest " 
for its eggs. 

The deep ocean floors have no plants. They are in- 
habited by a considerable variety of animals, such as fish, 
crabs, shellfish, starfish, etc. ; but the forms of life are here 
much less varied and less numerous 
than in the shallower waters near the 
shore. 

The animals of the deep sea live under 
enormous pressure, even several tons to 
a square inch. But just as land animals 
have air within their bodies, and thus 
withstand the pressure of the atmosphere, 
so sea animals are permeated by fluids, 
and thus unconsciously support the heavy 
pressure of the ocean. 

While many deep-sea animals are 
blind, it is curious that some have well- 
developed eyes, and are ornamented by 
colors in elaborate patterns. Hence there 
must be some light in the ocean abysses. It may be sup- 
plied by phosphorescent animals, of which there are many 
kinds in the deep sea. 




Fig. 56. —Deep-Sea 
Crustacean. X }. 



90 



PHYSICAL GEOGRAPHT. 






The intermediate depths of the ocean, between the upper 
part and the bottom, are prevailingly without life — a great 
desert space, cold, quiet, and mono- 
tonous. 

The shallow waters of the ocean 

margin teem with plants and animals. 

Many animals, such as sponges, 

5,-j corals, and barnacles, are fixed to the 

bottom ; they need not move about in 

t-«.<=^4^'W seaich for food, because the moving waters 

j'fJ/Ti bring it to them. Nearly all the plants of 

■■^f^ the sea are of a comparatively simple kind, 

If^i^Mfj without flowers or seeds. The shallow waters 

aie the fishing grounds of the sea, and furnish 

impoitant supplies of food to the neighboring 

lands. 





The animals of the shallow sea margins ex- 
hibit gi eater variety from place to place than is 
found among those of the open surface or of the 
deep floor. A notable peculiarity of the shallow 
waters in the polar regions is an abundance of 
seaweeds similar to those of low latitudes ; while 
the plants that grow on Arctic lands, chiefly mosses and 
lichens, are very unlike the land plants of warmer latitudes. 



CHAPTER V. 
THE LANDS. 

The Changes of the Lands. 

The form of the lands varies greatly from place to place. 
Here we find endless variety, in contrast with the wonder- 
ful uniformity prevailing in the oceans. As a result of 
this variety, thg conditions of life are very different for 
people on broad plains far inland, in deep valleys among 
lofty mountains, near haTbors of the seacoast, or on lonely 
islands in mid-ocean. The people of a savage tribe, living 
in any one of these homes and knowing little or nothing 
of the rest of the world, might contentedly remain ignorant 
of the way in which the forms of the land around them 
were produced. The people of a civilized nation, learn- 
ing much about all parts of the world from explorers and 
travellers, and perceiving that the way in which the people 
of different nations live is largely controlled by their geo- 
graphical surroundings, naturally inquire about the origin 
of highlands and lowlands, of mountains and valleys. 

During the nineteenth century, land forms have been 
studied attentively and much has been learned about their 
origin. The most important general result of this study 
is that the forms of the land as we now see them are found 
to be the effect of slow changes continued for thousands 
and thousands of years. It is at first difficult to realize 
that the crust of the earth, seemingly so solid, neverthe- 



92 PHYSICAL GEOGRAPHY. 

less slowly rises or falls, now revealing the bottom of a 
shallow ocean border as a land surface, now submerging a 
low continental border beneath the sea; but there can be 
no question that such movements have repeatedly taken 
place, and that they are even now in slow progress. It is 
hard to believe that deep valleys have been worn between 
high mountain ridges by nothing more than the long- 
A3ontinued action of rills and streams such as are still at 
work ; but the attentive observer must notice that active 
streams wear their channels, and receive the waste of the 
land that is washed from the enclosing valley slopes ; and 
great results must follow from these processes if they are 
long continued. The more the world is studied, the more 
certain it becomes that changes of these kinds are ordinary, 
not extraordinary, events in the history of the earth. 

The time required for all these changes can hardly be 
calculated ; it must be vast beyond comprehension. All 
the centuries of human history are only long enough to 
discover small changes in land forms. The lowlands that 
guided the migrations of the early races of men across the 
continents, and the mountains that stood in their way, are 
lowlands and mountains still; yet in the history of the 
earth lowlands have over and over again been slowly up- 
lifted to mountain height, and mountains have repeatedly 
been very slowly worn down to lowlands. Such changes in 
the expression of the face of the earth must have required 
periods of many million years, compared to which man's 
life on the earth is but a brief interval. But only when 
the forms of the land are recognized as the result of long 
changes can the lands be properly understood as the home 
of man. 



the lands. 93 

Physical Features of the Lands. 

Area of the Lands. — The globular earth is uneven 
enough to raise somewhat more than a quarter of its sur- 
face slightly above the oceans in broad land areas, called 
continents. The continents, covered only by the atmos- 
phere, present many contrasts to the deep sea floors cov- 
ered by the oceans; and these contrasts have for long 
ages been of the greatest importance in determining the 
geographical conditions of animal and vegetable life on 
the globe, as they have in recent ages determined the 
geographical conditions of man. 

The area of the globe is about 197,000,000 square miles. 
The lands occupy somewhat more than 50,000,000 square 
miles ; their total area remains uncertain until the polar regions 
are fully explored. Six-sevenths of the, land area are in the 
land hemisphere, where the ocean occupies little more than 
half the surface. The lands in the water hemisphere occupy 
only about one-fifteenth of the surface. 

The greatest islands are near the continents, as in the 
archipelago north of North America, the West Indies, New- 
foundland, the British Isles, and the Malayan-Australasian 
archipelago. Most of these islands stand upon continental 
shelves, and are separated from the continents only by shal- 
low water. The numerous oceanic islands, distant from con- 
tinents, are of small "total area (about 40,000 square miles). 

The five continents differ greatly in size, arrangement 
of parts, and degree of separation. It is not possible in 
the present state of knowledge to give a precise definition 
of a continent, other than to say that it is a large area of 
land. 



94 



PHYSICAL GEOGRAPHY. 



Asia and Europe form a single continent, often called 
Eurasia ; but on account of their great extent, and still more 
because of their great differences with regard to human his- 
tory, it is convenient to regard each of them as a "grand 
division " of land. 

Height of the Lands. — The highest mountain peaks, 
25,000 to 29,000 feet, do not rise above sea level so much 
as the greatest ocean depths sink below it, and the aver- 
age elevation of the lands (2400 feet =735 meters) is 
much less than the average depth of the oceans. 



METERS 
;,000 



4,000 



4,000 



Fig. 58. — Height of Land and Depth of the Sea. 

Fig. 58 exhibits the share of high and low land, and of 
deep and shallow ocean, the whole area of the earth being 
measured by the breadth of the figure. It is thus seen that 
most of the land surface is but little above sea level, while most 
of the sea floor lies deep below the sea surface. 



30,0UU • 






r 


20,000 ■ 








10,000 • 










LAND 




SEA LEVEL 



10,000 


\ 


OCEAN 


20,000 
30,000 - 






^^ "^^^ 



Continental Outline. — Africa and South America are 
similar in having simple outlines, with few large bays, 
peninsulas, and outlying islands. North America and 



TSE LANDS. 95 

Eurasia are alike in having irregular outlines, with many 
large bays and peninsulas, and with numerous outlying 
islands. Europe is rich in arms of the sea entering far 
into the land, like the North, Baltic, and Adriatic seas. 

Continents are generally broader in the north than in the 
south. This is distinctly seen in South America, North Amer- 
ica, and Africa. Land arms are more frequently directed 
southward than northward, as in Florida and Lower Califor- 
nia, and in many peninsulas from Spain to Farther India. 

The grouping of the continents is very irregular and follows 
no known law. The lands occupy an irregular belt stretching 
from Cape Horn to Cape of Good Hope, broad across the mid- 
dle of the continents, narrow at their ends, broken at Bering 
Strait, and with a half-submerged arm reaching out to Australia. 

The earth as a whole, being of globular form, may be 
treated as a body of regular shape, its different parts from 
equator to poles being marked off by a simple system of paral- 
lels and meridians. The atmosphere, covering the entire earth, 
may be for the most part treated in belts, the members of the 
wind system and other climatic features being arranged nearly 
parallel to the equator, but made somewhat irregular by the 
interference of the continents. 

The ocean, covering the greater part of the earth, exhibits 
a well-marked system of surface movements that are roughly 
symmetrical on both sides of the equator. The lands are so 
irregularly distributed and so uneven in surface that no simple 
description can be given of their outline or their form. 

Changes of Continental Outline. — The form of the lands 
and the outline of their shores seem at first sight to be 
unchangeable. But the more the world is studied, the 
more certain it becomes that slow changes are going on in 
the shape of the earth's crust, and that the outline of the 
continents is subject to change as the continental masses 



96 PHYSICAL GJEOGRAPHT. 

very slowly rise or sink. Thus in the course of long ages 
the geography of the world may be greatly altered. 

Slight movements of elevation or depression, such as have 
often happened in the earth's long history, may slowly drown 
a lowland on a continental border, or gradually reveal a part 
of a continental shelf as a plain bordering higher land. 
These movements are so slow that they are hardly percep- 
tible in the course of a century ; but when continued for 
hundreds of centuries they cause changes of great importance 
in the geography of the lands. 

It has been discovered that a large part of North America 
had a land existence at an early stage in the earth's history, 
uncounted millions of years ago, and that it was afterwards 
submerged ; for wide-spread rock layers formed of bedded 
sediments and containing fossils of sea animals are found 
overlying and burying an ancient land surface with hills and 
valleys. In still later times the continent has suffered many 
small changes of altitude, sometimes sinking so that a sea of 
moderate depth overspread its borders, sometimes rising again 
so that the land extended beyond the present shore line, but 
in a general way retaining its ancient outline. 

The same may be said of a considerable part of Eurasia, 
and of certain parts of other continents. Hence it is coming 
to be believed that, on the whole, continents are elevations in 
the earth's crust that have for long ages stood higher than 
the deep ocean floors. 

Changes in continental outline are so slow that they 
have seldom been detected by direct observation ; but this 
is chiefly because delicate observations of shore lines have 
been made only within the last century or two. 

If the ancients had been as attentive to geographical as to 
astronomical problems, it can hardly be doubted that many 



THE LANDS. 97 

distinct changes in the level of the land and in the position of 
shore lines would have been found between the time of ancient 
G-reece and to-day. 

Observations in the last hundred years or more give reason 
to believe that the coasts of Massachusetts and New Jersey 
are now sinking (one or two feet a century), and that much 
of the_ coast of Sweden is rising (maximum, three feet a cen- 
tury). The coast of the Netherlands is sinking a foot a 
century, and its fields near the shore, 15 to 20 feet below the 
sea level, are diked to keep the water off. - Many geographical 
proofs of change of level will be given in later pages. 

The globular form and regular rotation of the earth as 
a whole seem to be permanent features of our planet. The 
belt-like arrangement of the winds seems to be as enduring 
as the shining of the sun. The eddying of the oceans 
must be affected by the outline of the continents ; yet as 
long as the sun shines, the earth rotates, and the winds 
blow, the eddies must turn regularly to the right or left, 
according to their hemisphere. But the outline of the 
lands is subject to many changes that seem to be without 
system. 

There will always be doldrums around the equator, and 
westerly winds in temperate latitudes. There will always be 
a current entering the torrid zone on the eastern side of the 
oceans. But in other ages Asia and Europe may have been 
or may come to be separated by the submergence of the plains 
from the Black Sea to the Arctic; and Asia and Australia 
may be united by the elevation of the sea floor between them. 
Hence, although the continents seem to be the most perma- 
nent features of the earth's surface, they may be long outlived 
by the systematic movements of the ocean currents and the 
winds. 



98 PHYSICAL GEOGBAPRY. 

Variety of Land Surface. — The surface of the continents 
possesses great variety of form and composition, in strong 
contrast to the monotony of the broad sea floors. Rocks 
and soils, as well as mountains, valleys, and plains, differ 
from place to place. Peaks and ridges of resistant rocks, 
slopes and valleys underlaid with weak rocks and covered 
with soils of gravel, sand, and clay ; these and many other 
differences give great variety to the lands. 

Mountain ranges are characteristic of the continents 
rather than of the sea floors, where plains of vast extent 
prevail. But mountain ranges occasionally rise from the 
sea bottom, showing their crests above the surface, as in 
the West Indies. Submerged ranges may yet be discov- 
ered by soundings among the island groups of the Pacific. 

The continental shelves overlapped by some of the oceans 
have something of the variety of the lands from which they 
receive washings of gravel, sand, and clay. Volcanoes and 
their lavas are among the few features possessed in common 
by the deep sea and the dry lands. 

Climate of the Lands. — The conditions of the land sur- 
face vary greatly under different conditions of weather and 
climate. Heavy rains are followed by clear sky; strong 
winds by light winds or calms. A bare desert surface in 
the torrid zone may be heated at noon above 150°, and 
may cool nearly to freezing the next night. In the frigid 
zone the frozen soil may thaw and warm at the surface 
during summer, but it will be intensely frozen again, even 
to 80° below zero, the next winter. 

Variations of temperature, so distinct at the land surface, 
rapidly decrease under ground. Af; a depth of 4 or 5 feet 



THE LANDS. 99 

daily changes are hardly perceptible ; at a depth of 20 or 30 
feet there is but little variation from the mean temperature 
of the year (about 80° in the torrid zone, near zero in far 
northern lands). 

In northeastern Siberia, where the ground is frozen to a 
depth of 300 to 500 feet, grass and bushes grow when the soil 
thaws for a few feet in summer ; but large trees are wanting. 
The mammoth, an animal resembling a hairy elephant, but no 
longer found living, has sometimes been preserved in the frozen 
beds of sand and gravel that border some of the Siberian 
rivers, where it was buried at the time of river floods centuries 
ago. 

On descending beneath the land surface, as in deep mines, 
the crust of the earth is found to be about 1° warmer 
for every 60 feet of descent ; but this rate varies in differ- 
ent regions. Hot springs, geysers, and volcanoes all indicate 
the occurrence of high temperatures deep under ground ; 
hence it is believed that the great body of the earth beneath 
its cool outer part or crust is glowing hot, and less rigid than 
if it were cold. In spite of the great store of heat within, 
the temperature of the surface is hardly affected by that of the 
interior, but depends almost wholly on sunshine. 

Activities of the Lands. — In nothing do the continents 
differ more strikingly from the sea floors than in the activ- 
ity of the various processes that go on upon the lands, and 
in the rapidity of the changes that the processes produce. 
The surface rocks split apart when water freezes in their 
crevices, or they rust under the chemical action of air and 
water. A sheet of loosened rock waste is thus formed 
over most of the land surface. The various processes by 
which rock waste is produced are known under the gen- 
eral term weathering. Weathering varies greatly under 
different climates and with different rocks. 



100 



PHYSICAL GEOGRAPHY. 



In the dry, mild, and equable climate of Egypt, ancient 
statues have been but slightly weathered in several thousand 
years. A great stone monument, 60 feet high, known as Cleo- 
patra's Needle, brought from Egypt to New York in. 1880, was 
so much affected by the weather in a single winter that it was 
necessary to coat its surface with a preservative substance. 

In Egypt it had stood 
over 3000 years with 
little change. 

Under the heavy 
rainfall and luxuriant 
vegetation of the equa- 
torial forests, weather- 
ing advances with com- 
parative rapidity ; it is 
aided by the products 
of decomposing vege- 
table matter. On ex- 
posed mountain peaks 
and in high latitudes, 
where the temperature 
frequently rises or falls 
past the freezing point, frost is active in splitting rock masses 
to smaller and smaller fragments. 

Although acting slowly, weathering accomplishes great 
results in the long course of the earth's history. The occur- 
rence of soil, in which the roots of so many useful plants 
grow, and the form of the land surface, which constantly 
exerts so great an influence on the manner of man's living, 
are both due in large part to the work of the slow but 
persevering attack of the atmosphere on the rocks of the 
lands. 

Every rock ledge or quarry offers opportunity for observing 
this widespread process. The weathering of the older grave- 




Fig. 59. — A Quarry showing Weathered Kock. 



THE LANDS. 



101 




Fig. 60. — Granite. 



stones in cemeteries may frequently be noticed. In cities the 
different amounts of weathering on old and new stone build- 
ings, or in buildings of different kinds of stone, serve to illus- 
trate in a simple way the 
changes that occur on a 
much greater scale all over 
the lands. 

Varieties of Rocks. — 

The rocks of the earth's 
crust are of many differ- 
ent kinds, and vary 
greatly in their resistance 
to weathering. Granite, 
consisting of crystalline 
grains of several min- 
erals (quartz, feldspar, 
and mica) closely bound together, is one of the more 
resistant rocks ; but the weathering of one of its minerals 
(feldspar) unbinds its parts, and it slowly crumbles to a 
gravelly soil. 

Quartz is easily recognized by its glassy lustre and its hard- 
ness. It will strike fire with steel, and was employed for this 
purpose before matches were invented. Feldspar is not quite 
so hard; its color is usually gray or pink, and it splits with 
a smoother face than quartz. Mica has the property of split- 
ting into very thin elastic scales. 

Sandstone, composed chiefly of grains of quartz, is resist- 
ant when the grains are well cemented together, but weak 
when they are imperfectly cemented. 

Sandstone is formed from the waste of such rocks as gran- 
ite. The sand is washed into the sea or other body of water. 



102 



PHYSICAL GEOGRAPHY. 




Fig. 61. —Pebbly Sandstone. 



and is there spread out in layers which may in the course of 

ages accumulate to great thickness. Infiltering waters, carry- 
ing some mineral 
substance in solu- 
tion, deposit it be- 
tween the grains and 
bind them more or 
less perfectly to- 
gether. Pebbles are 
often found in sand- 
stones, giving them 
a coarse texture. 

The finer waste 
from such rocks as 
granite forms muddy 
deposits when it set- 
tles in quiet water. 
The grains are here 

much smaller than those of sandstone, and the rocks thus 

formed, known as shale and slate, are generally of small or 

moderate resistance. 

Shaly sandstone is a rock 

intermediate between a 

fine shale and a granular 

sandstone. 



Limestone is gener- 
ally formed of the re- 
mains of the shells or 
skeletons of sea ani- 
mals, more or less 
broken to fragments or 
even ground to powder 
in the waves of shallow waters. It often includes shells 
and corals as fossils, as in Fig, 62. It is not so resistant 




Fig. 62. — Limestone with Fossil Shells. 



THE LANDS. 103 

to the weather as granites or dense sandstones, and is 
much more soluble in water than other rocks. 

Some limestones are formed of the fine ooze that accumu- 
lates on the ocean bottom from the shells of minute animals 
like the globigerina (Fig. 38) that float near the surface when 
living. Limestone of this kind is called chalk. 

There are manj'- kinds of lavas that have been pushed 
out from the hot interior of the earth through the colder 
crust. Basalt, a dark and dense lava, is one of the most 
resistant rocks of this kind. 

When lavas are blown with explosive violence from vol- 
canoes, they are shattered to fragments. Deposits formed of 
such fragments may be much less resistant to weathering than 
heavy sheets of dense lava that, after flowing quietly from a 
volcano, solidify as they cool. 

The Wasting of the Lands. — Surface water, supplied 
by rain or melting snow, washes the finer rock waste down 
the slope of the land to the valley floors or to the streams, 
and the streams bear the waste along their channels, thus 
sweeping it from one place and spreading it over another, 
or washing it to the sea. Where streams run, they rasp 
their channels with the rock grains that they bear along, 
and valleys are thus slowly worn in the surface of the 
land. The higher the land, the deeper the valleys may 
be cut. 

Large valleys, receiving many smaller branching valleys 
and ravines that dissect the surface of the land and lead 
streams from higher to lower ground, are among the most 
characteristic features of the continents. They are the result 
of stream action, and cannot occur on the deep sea floor. 



104 PHYSICAL GEOGRAPHY. 

They are sometimes found beneath sea level, extending for- 
ward from the present coast line across the shallow conti- 
nental shelf ; they are then taken as proof of the depression 
of that part of the continent. 

The winds act with great effect on bare surfaces, sweep- 
ing finer rock waste into drifts (dunes), and raising the 
dust aloft to settle far away. Waves, currents, and tides 
wear the edge of the land and the shallow continental 
margins, cutting cliffs and building sand reefs along the 
shores. 

The wet-weather streams of roadsides and the waves on 
the shores of ponds or reservoirs exhibit in a small way the 
processes characteristic of large rivers and oceans. The dif- 
ferent effects of winds on dusty roads, on grassy fields, or on 
forested surfaces, illustrate the contrast that prevails between 
wind action in dry and in moist regions. 

The sea floor is enduringly quiet and silent. The tides of 
the deep sea are very faint. The creeping of cold polar water 
towards the equator must be almost imperceptible. Chemical 
changes of the bottom deposits are slight. The gain of the 
bottom by the steady shower of organic remains from the sur- 
face must be very feeble, and the change of form by this gain 
must be exceedingly slow. 

Although the changes produced in the form of the lands 
by weathering and washing are slow, they have been so 
long continued that marvellous results have, been pro- 
duced. Not only are the lands dissected where deep 
valleys have been worn in plateaus and mountains, but 
whole mountain ranges have been worn down to lowlands. 
The forms of the land to-day can be appreciated only 
when it is seen that they are the present stage of a long 
series of changes. The description and explanation of 



THE LANDS. 105 

land forms thus considered is the object of the greater 
part of this book. 

The general wasting of a land surface is slow, but local 
changes are easily noted by the attentive observer. Roads are 
gullied by wet-weather streams. Much soil may be washed 
from a plowed hillside in a single rainstorm. Landslides pro- 
duce striking changes on mountain slopes and in the valleys 
below. Cataracts like Niagara wear back their cliffs even more 
than a foot a year. Deltas grow forward into lakes and seas 
so as to gain perceptibly in a century. Ostia, once the port of 
ancient Rome, is now over a mile inland from the advancing 
front of the Tiber delta. Sea cliffs may be cut back by the 
waves ; the exposed eastern bluff of Cape Cod, Mass., is 
retreating at an average rate of three feet a year. 

The general process of wasting and washing, by which the 
surface structures are slowly worn away and the deeper and 
deeper structures of the earth's crust are attacked, is called 
denudation, or erosion. Its rate varies greatly with rock struc- 
ture, slope, and climate. The lower Mississippi carries enough 
land waste to. lower its whole basin an inch in about three 
centuries. An inch in from one to ten centuries may be taken 
as a rough value of denudation averaged for large areas. 

Opportunity for Varied Forms of Life. — The land sur- 
face, unless too cold, too dry, or too bare of rock waste 
(soil), is well covered with vegetation, the larger part of 
which consists of flowering plants, much more highly 
organized than the plants of the sea. 

Land plants gain their food from the soil through their 
roots, and from the atmosphere through their leaves, and thus 
utilize the rock waste and the air with which the rock crust of 
the land is covered. Sea plants make little use of the deposits 
gained by the sea margin, and take their food chiefly from 
minerals and gases dissolved in sea. water. 



106 PHYSICAL GEOGRAPHY. 

Land animals are numerous, varied, and as a whole 
highly organized. They exceed the animals of the deep 
sea floor in variety of structure and habit. They are 
exceeded in number only by the animals of the shallow 
sea margins or of the open sea surface. 

Many animals of the sea are attached to the bottom, like 
corals ; others move slowly, like starfish and shellfish ; still 
others float with the drifting waters, having little movement 
of their own, like jellyfish. Only the more highly organized, 
like many fish, swim rapidly. But nearly all land animals 
move about actively, walking, running, or flying. 

The larger and more important land animals (mammals 
and birds) are warm-blooded. The only warm-blooded ani- 
mals of the sea (whales, porpoises, etc.) are believed to be 
the descendants of remote land ancestors, gradually modified 
for marine life, but retaining many resemblances to the forms 
from which they are derived. 

The rock waste of the land has come to be the dwelling- 
place of certain forms of land life, such as earthworms, many 
kinds of insects, and certain mammals, like the moles. Many 
animals, such as ants, many kinds of bees and wasps, prairie 
dogs, foxes, etc., burrow in the finer waste. Other animals, 
such as snakes, find shelter in the hollows between coarse 
fragments of rock waste. 

Apparently owing to the greater mobility of air than of 
water, many land animals have developed organs for the pro- 
duction of sound, the most remarkable sounds being the songs 
of birds and the speech of man. The animals of the sea are, 
with hardly an exception, silent. 

Floating and swimming sea animals are of about the same 
weight as the water that they displace. Birds and insects are 
much heavier than the air in which they fly ; and flying must 
be regarded as indicating a much higher development than 
swimming, . . 



THE LANDS. 



107 




The higher development and the much greater intelli- 
gence of many land animals than of sea animals should 
be regarded as a result of the greater variety of physical 
conditions found on the lands than in the seas. 

The class of insects, almost limited to the lands, furnishes 
many examples of extraordinary instinct, as with bees and 
ants. Nest building by birds, house building by beavers, 
" homing " of pigeons, 
and trailing (by scent) 
of dogs, are examples 
of highly developed in- 
stincts that have no 
parallel among the in- 
habitants of the sea. 

The physical condi- 
tions of the deep sea are 
more varied than those 
of the lands only in 

respect to the variations of pressure. Land animals are sub- 
ject at sea level to an atmospheric pressure of about a ton to 
the square foot of surface. This pressure decreases with 
altitude, but few animals climb or fly high enough to reduce 
it by half. In the sea the pressure is increased a ton per 
square foot by descending a little more than 30 feet; and 
many sea animals have a vertical range of much greater 
measure. 

Distribution of Life. — The distribution of plants and 
animals can be explained only when it is understood that 
the members of every living species are descended from a 
long line of ancestors. Related species, such as the vari- 
ous antelopes or the hawks, are believed to have sprung 
from a single species ; their existing differences are due 
to gradual variations by which they have become better 



Fig. 63.— Beavera. 



108 



PHYSICAL GEOGRAPHY. 




Fig. 64. — Caribou. 



adapted to their slowly changing surroundings through 

long ages of the earth's history. 

Among the many changes of surroundings none have 

been more important than variations in the outline and 

form of the lands such as may 
have been caused by the slow 
raising or wearing down of 
mountain ranges, or by the 
slow elevation or depression of 
a continental border. Conti- 
nents, once connected, may have 
been divided by the depression 
and submergence of the lower 
lands; the descendants of a 
common stock would then be 
separated into two families. 

The longer the time since such a separation, the more the 

descendants of one family may vary from those of the other. 
For example, the reindeer of northern Europe and the 

caribou of far northern Amer- 
ica are so much alike that a 

recent connection of the lands 

on which they are found must 

be inferred. Again, the puma 

and jaguar of middle latitudes 

in the New World are cat-like 

animals, and resemble the lion, 

tiger, and leopard of similar 

latitudes in the Old World in 

so many ways that naturalists have been led to believe they 

must be descended from the same stock. Hence in some 




'^^Jw. 



Fig. 65. — Jaguar. 



THE LANDS. 



109 




rig. 66.— Tiger. 



former time the Old and New Worlds must have been 
connected in latitudes where the ancestors of these ani- 
mals could pass from one 
region to the other. But 
the American forms are 
now so unlike the others 
that a long time must have 
elapsed since the continents 
were separated. 

Life on Islands. — Islands that rise from continental 
shelves are occupied by many plants and animals similar 
to those of the neighboring main- 
land. It is inferred from this that 
the continental mass once stood 
higher, and that the continental 
shelf was then a lowland on which 
the present islands rose as hills or 
mountains. 




Various species of cassowaries 
(ostrich-like birds) are found in 
Australia and the islands to the 
north, each land area having its own 
species. Erom this it is argued that 
the common ancestors of all these 
species occupied the region when the 
continental mass stood higher and 
the mainlands and islands were connected by the lowland of 
the present continental shelf. Since then the region has 
been depressed, the lowland flooded by the sea, and the islands 
separated from Australia and from each other. The differences 
between the various species of cassowaries must have arisen 
since they were separated by the drowning of the lowlands. 



Fig. 67. — CaBSOwary. 



110 



PHYSICAL GEOGRAPHY. 



Australia, the most isolated continental region of the east- 
ern hemisphere, has no true mammals but is the chief home 
of marsupials (pouched mammals), like the kangaroo, once 
widespread over the world, as is shown by their fossils in rock 
layers, but now hardly surviving elsewhere. ISTew Guinea and 
several other islands north of Australia, separated from the 
mainland by a shallow sea, are also occupied by similar mar- 
supials, thus confirming 
the recent connection of 
these lands as indicated 
by the cassowaries. Asia 
has no marsupials, but 
many large mammals. 
The neighboring islands 
on the southeast, rising 
from a broad continental 
shelf, possess many sim- 
ilar mammals; hence 
here also the islands must 
have been recently con- 
nected with the continent. 
But the Asian and Australian regions must have been long 
divided, as their animals are very unlike ; the division must 
have followed the deep-water line between Celebes and aSTew 
Guinea, known as '' Wallace's line," from its discoverer. 

An island is so distinctly separated from the rest of the 
lands, that the Latin word for island (insula) gives us the 
words "insulate" and "isolate," meaning to place apart or 
alone. 




Fig. 68. — Kangaroo. 



Islands that rise from the deep ocean floor far from the 
continents have no large native animals, but are occupied 
by such forms of animals and plants as might have readied 
them by flying, swimming, or floating from the nearest 
larger land. 



THE LANDS. Ill 

The Azores, a group of mid-ocean volcanic islands in the 
North Atlantic, are so called from the hawks that were com- 
mon upon them when they were discovered by voyagers from 
Europe. The Galapagos islands, of similar origin, in the 
Pacific west of Peru, are named from the tortoises that abound 
upon them. 

Races of Man. — The homes of the races of man, together 
with their remarkable differences of language, religion, and 
form of government, correspond in a general way to the 
division of the lands into continents. Hence it may be 
believed that the separation of the continents by the oceans 
has been the chief cause of the division of mankind into 
several races. 

Through the greater part of man's existence on the earth 
his condition has been uncivilized, and his migrations have 
been of the primitive sort now seen among peoples still sav- 
age or barbarous, like the wandering Bedouins of the Sahara, 
or the forest tribes of the Amazon basin. Thus distributed, 
man has come to be divided into several races, with many 
branches, stocks, and families. It should not be assumed that 
all mankind can be divided into a few well-defined races. 

The greatest of the continents, Eurasia, contains two 
races. The European race, generally white but with 
some dark-skinned families, has its home in Europe, 
part of Africa north of the Sahara, and southwestern 
Asia. The leading nations of this race are the most 
advanced peoples of the world, having developed liberal 
governments in which the rights of the people are con- 
sidered, and having advanced greatly in the cultivation of 
the arts and sciences. 

The Asian race is found in northeastern Asia; it is 
often called the Yellow race. China contains the greatest 



112 PHYSICAL GEOGRAPHY. 

number of this people. Although comparatively advanced 
in many arts, the Asians have acquired little knowledge 
of the sciences, and their governments are usually despotic. 
America is the home of the American or Red race ; its 
people is divided into many tribes, each of which is gov- 
erned by a chief. Africa is the home of the African or Black 
race, governed by despotic kings or chiefs. Australasia and 
the peninsulas and islands of southeastern Asia include a 
number of less important races. Few nations among these 
races have made important advances toward civilization. 

Within the last few centuries the means of ..travel over land 
and sea have greatly increased, and to-day the races of man- 
kind are by no means limited to the continents named above 
as their homes. People of European ancestry are now the 
chief part of the population in North and South America, 
southern Africa, Australia, and ISTew Zealand, as well as in 
Europe. The Chinese are by no means limited to northeast- 
ern Asia, but are found in large numbers as merchants and 
laborers in southeastern Asia, Australia, and elsewhere. 
Many of the African race are now living in North and South 
America. 

It should be noticed that, while the people of the European 
race are now widely distributed over all parts of the world, 
and while Asians and Africans are found in large numbers 
in other lands than their homes, none of the less advanced 
races have migrated into Europe. 



CHAPTER VI. 
PLAINS AND PLATEAUS. 

The Geographical Control of Population. 

Southern New Jersey. — If a traveller should descend 
from the uplands of southeastern Pennsylvania, cross the 
Delaware, and proceed over the lowlands of southern 




Fig. 69. — Southern New Jersey. 



New Jersey to the seashore, he might discover that many 
geographical features, such as the forms of the land, the 
arrangement of the streams, the mineral products, and the 



114 PHYSICAL GEOGRAPHY. 

soils, are here grouped in belts, roughly parallel to the 
coast line, as in Fig. 69. The upland belt on the border 
of Pennsylvania has a rolling surface, diversified by nar- 
row vallej'^s. The soil is good, and most of the upland is 
cleared for farming. The rock beneath the soil is firm 
and enduring; quarries are easily opened on the valley 
sides, and many of the older farmhouses and barns are 
built of stone thus provided. The streams afford water 
power for mills, in which grain from the farms is ground. 
A number of good-sized towns on the Delaware have 
profited from the easy transportation afforded by river 
steamboats. The open valley of this large river has long 
been an important path of travel, a century ago by stage, 
now by rail, on the line connecting the important cities 
of Washington, Baltimore, Wilmington, Philadelphia, 
Trenton, Newark, and New York. Next beyond the 
Delaware there is a narrow lowland belt, free from firm 
rocks but deeply underlaid by fine clay. Crockery, earth- 
enware, terra-cotta, and bricks are made here for domestic 
and industrial uses. Then follows a belt of slowly rising 
ground ending in low hills, the most uneven part of south- 
ern New Jersey. The headwaters of many short streams 
rise among the hills and run northwest to the Delaware ; 
between the streams the slope from the hills includes 
much good farming country, and here are the best farms 
in the southern part of the state. Beds of marl (limy 
clay) occur in this belt, frequently containing shells of 
sea animals. The marl is often dug out to serve as a 
fertilizer on less productive soils. 

The long gentle slope that leads from the hilly belt 
southeast to the ocean has for the most part a deep sandy 



PLAINS AND PLATEAUS. 



115 



soil generally overgrown with pine forest, and so infertile 
as to be hardly worth clearing. Here the population is 
scanty. The surface is so flat that roads, and railroads 
run for long distances on straight lines. Not a hill is to 
be seen for many miles. A house or tower that rises over 
the tree tops discloses " an unbroken extent of dark-green 
pine forest as far as the limit of vision, stretching away in 




Fig. 70. — The Beach, Atlantic City, New Jersey. 

long, gentle swells," nearly as level as the ocean itself. 
The streams flowing southeast are sluggisli, and afford 
little or no water power. The boggy soil of their marshy 
valleys is sometimes used for the cultivation of cranber- 
ries. Nearer the shore the plain is somewhat interrupted 
by shallow valleys, and its surface is more generally cleared 
and farmed. Short arms of the sea enter the lower valleys, 
giving harborage for small vessels, and many fishermen 
live in the shore villages, A belt of shallow salt-water 



116 PHYSICAL GEOGRAPHY. 

lagoons with extensive marshes of reeds border the main- 
land for a breadth of about five miles. Finally come the 
sand reefs, half a mile or more wide, enclosing the lagoons. 
The surface of the reefs is occupied by gently rolling sand 
hills drifted by the wind; the ocean border is smoothed' 
into a broad beach by the heavy surf. Here thousands of 
persons from the interior of the country spend their sum- 
mer vacations, enjoying the mild temperature of the sea 
breezes, bathing in the surf, and sailing and fishing in the 
quiet waters of the lagoons, or on the rougher waters of 
the ocean. 

This simple example serves to illustrate the way in 
which the physical features of a district exercise a control 
over the distribution and occupations of its peoj^le. It is 
not by accident that a large population has gathered on 
the interior lowland belt, but because of the advantage 
given by good soil on an open surface where movement 
from place to place is easy. Many other examples of the 
same kind may be found by the intelligent observer in 
various parts of the world. The careful study of geog- 
raphy therefore requires a good understanding of differ- 
ent kinds of land forms, as well as a knowledge of their 
soils and their products, in order to make clear the rela- 
tion between man and his geographical surroundings. 

The best method of gaining an understanding of land 
forms is to study their origin. It would be easier to 
remember the features of the successive belts described in 
the preceding paragraphs if some explanation were given 
of the way in which they have been produced. Explana- 
tion as well as description is therefore important in 
physical geography. 



plains and plateaus. 117 

Coastal • Plains. 

Introductory Example. — In certain parts of the world 
the hills bordering a mountain range descend directly to 
the seashore. Waves beat on the headlands, cutting cliffs 
in their front. The larger rivers build deltas at their 
mouths, and here the sea is bordered by low land. The 
rock waste from the mountains and cliffs furnishes much 
sediment for the smooth sea bottom. 

This means that while the land has been worn and 
roughened by the action of weather and streams, the sea 
floor has been smoothed by the gain of land waste. The 





Fig. 71. —Mountains bordering the Sea. 

depth and number of the valleys show that already much 
waste has been carried into the neighboring seas. The 
dredge brings up gravel, sand, and mud from the sea bot- 
tom, the texture of the sediments being finer as distance 
from land and depth of water increase. 



118 PHYSICAL GEOGRAPHY. 

A rugged land like this seldom supports a large population. 
It is only in the valleys that strips of flat land, suitable for easy 
occupation, can be found. Most of .the population is gathered 
in villages near the mouths of the large rivers. Eoads cannot 
easily follow the shore, for many of the cliffs are washed to 
their base at every high tide. In passing from one valley 
village to another the traveller must climb over a ridge. 
Many dwellers in the shore villages are seafarers and fisher- 
men, although there are few protected harbors, for the shore 
line is comparatively straight. 

The coast of California presents many stretches of this kind. 
The Sierra Santa Lucia, south of Monterey, descends boldly to 
the sea, its spurs being cut off in great cliffs. The shore is 
thinly inhabited for a distance of 70 miles. 

The Mediterranean coast from Nice past Genoa to Spezzia 
is a famous example of this class, more densely populated than 
usual. The mountain spurs rise rapidly from the water's edge; 
the streams run like torrents to their very mouths. Little 
villages nestle in the indentations of the coast, but their fish- 
ing boats are unprotected in on-shore storms. The harbor of 
Genoa is enclosed by an artificial breakwater. A railroad fol- 
lowing this rugged shore is compelled to tunnel through many 
headlands. No highway has yet been made along the shore 
east of Genoa. Westward from Genoa to Nice, only with great 
difiiculty and at great expense has a famous highway been 
constructed aroimd or over the headlands. 

Narrow Coastal Plains. — Fig. 72 exhibits a region 
where the foothills of the mountains descend to a low- 
land, and the lowland slopes gently to the sea. Such a 
lowland is called a coastal plain. The gentle slope of the 
plain is continued in the slowly deepening sea floor. The 
form of the land may here be much more favorable to 
human occupation than in the previous example. 

The plain is divided into many similar strips by the 
shallow valleys of streams that flow across it from the 



PLAINS AND PLATEAUS. 



119 



mountains. Each strip of the plain is so smooth and so 
nearly level that a great part of the rainfall enters the 
open soil, instead of running off in streams. The plain is 
built of layers of gravel, sand, and clay, the uppermost 
layer forming the surface of the plain. The pebbles in 




Fig. 72. — Karrow Coastal Plain. 

the gravel often resemble the harder rocks of the hilly 
background ; the clay often contains shells similar to those 
found in the neighboring sea. 

Ravines are worn by wet-weather streams in the side slopes 
of the plains between the larger valleys. Even the larger val- 
leys have been carved by the rivers that flow through them. 
In the future the plain will be more dissected; in the past it 
was less dissected. Before any valleys were cut the different 
parts of the plain were all united in a continuous, even surface. 

In view of all this it must be concluded that the coastal 
plain was once part of a shallow sea bottom, and that this 
region was then like the sea-skirted mountains of the pre- 



120 PHYSICAL GEOGRAPHY. 

ceding example. Since then the relative level of the land 
and sea has been altered, and part of the smoothed sea 
bottom is now laid bare to form the coastal plain. 

As soon as this simple relation is recognized, the background 
of hills and mountains is seen to be the source of the rock 
waste of which the strata of the plain are built. The inner 
boundary of the plain is the former shore line. The rivers 
from the older land extend their courses across the new plain, 
guided by its gentle slope to the new shore line. Some small 
streams may rise on the plain and flow by shorter direct courses 
to the sea. 

As the region now stands higher than before, the rivers 
tend to wear down their valleys to the new level of the 
sea at their mouths ; the valley sides waste away, and thus 
the valleys slowly become wider ; but the streams cannot 
wear the valleys deeper than the surface of the sea at 
their mouths. The level of the sea is therefore called 
the baselevel of the region. As long as the land stands 
in its present position, continually wasting under the de- 
structive attack of the atmosphere, the plain surface will 
in the course of ages be worn lower and lower, closer and 
closer to the baselevel. In the coastal plain here figured 
a good beginning of this great task is accomplished along 
the line of the chief stream ; but the uplands between the 
valleys are as yet hardly touched. 

A simple method of describing land forms may be illus- 
trated by means of this elementary example. The exist- 
ing forms of the coastal plain must be treated as showing, 
first, something of the original form of the plain; and, 
second, the changes it has suffered under the attack of 
weather and water. In this example the smooth surface 



PLAINS AND PLATEAUS. 



121 



of the plain between the valleys still preserves the original 
form with insignificant change. The valley floors of the 
extended rivers and the narrow ravines of the side streams 
are changes from the original form. 



The surface of each part of the plain is everywhere so much 
alike in form and quality that villages may be located here 
and there upon it without system. Roads run in straight lines 
for long distances because they meet no obstacle. Boats on 
the larger rivers coming from the mountains in the background 
bring the products of mines 



and quarries, of forests and 
upland pastures. A city near 
the sea serves as a market 
for the agricultural products 
of the plain, although these 
are sometimes not of the best, 
for the sandy soils may be 
hardly worth tilling. 

Sand reefs or beaches may 
be formed by the waves a little 
distance off-shore, built of sands 
washed in from the sea floor at time of 
storms. The reefs are covered with dunes 
of sand blown up from the beach by the 
winds, and enclose quiet, marshy lagoons. 
Here or there the tide maintains a passage or inlet through 
the reef, and villages spring up on the mainland near by, 
whence fishermen go out in small boats to the shallow sea. 

The eastern coast of Mexico in the neighborhood of Vera 
Cruz is bordered by a low coastal plain (Fig. 73) about 50 
miles widcj back of which the mountains rise rather abruptly. 
The plain is called the " tierra caliente," or hot country. It 
is sandy, malarial, and relatively infertile. Vera Cruz, the 
chief port for the interior highlands, has a poorly protected 




Fig. 73. — Coastal 
Plain of Mexico. 



122 



PHYSICAL GEOGRAPHY. 



anchorage on the open shore. In the Mexican War (1847), 
when Vera Cruz was captured, the Mexicans found no other 
place for resistance on the smooth coastal plain, and therefore 
concentrated their forces on the hilly border of the old land. 

Here they entrenched 
themselves on a spur 
called Cerro Gordo, be- 
tween two ravines that had 
been deepened by streams 
from the mountains after the 
region was uplifted; and here- 
decisive battle was fought. 
3 uplands of the Dekkan in the 
peninsula of India (Fig. 74) are bor- 
dered on the east by a gently sloping 
coastal plain, not more than 50 miles 
wide. It consists of bedded gravels, 
sands, and clays containing marine or 
brackish-water shells. Large rivers, the 
Godavari and Kistna, draining great areas of 
the older land, have extended their course 
across the plain and built projecting deltas at 
its front. Madras,. the chief city of the plain, has 
Coastal Hain no harbor ; it is difficult or impossible to land from 
vessels during storms, except under the protection 
of an artificial breakwater. 

Broad Coastal Plains. — Fig. 75 represents a broader 
coastal plain than the preceding example. The outer 
part of this plain is much like the plain in Fig. 72 ; but 
the inner part is more cut by ravines, and the larger rivers 
have broader valleys than before. A greater change iii 
the relative height of land and sea is indicated by the 
greater height and breadth of the plain ; and a longer 
time since the elevation of the inner than of the outer 




Fig. 74. 



PLAINS AND PLATEAUS. 123 

part must be inferred from the greater amount of work 
done by the streams in carving their valleys and ravines. 

The strata of an extensive coastal plain are often of coarser 
texture near the former shore line, and of finer texture near 
the present shore line. During the slow uplift of the plain, 




Fig. 75. — Broad Coastal Plain. 

different kinds of sediments may have been laid down near 
the shore, as the sea retired from the plain. Hence the soils 
of such plains are commonly of different kinds in the inner, 
middle, and outer parts, being arranged in belts roughly 
parallel to the length of the plain. 

The Atlantic coastal plain of the southern states, of 
which a characteristic portion is included in South Caro- 
lina (Fig. 76), is roughly divisible, according to its form 
and soil, into belts parallel to the shore line. At the same 
time it is transversely divided into strips by the several 
large rivers that are extended from the back country 
(Piedmont belt), and by the many smaller branches of 
these rivers that rise on the plain itself. 



124 



PHYSICAL GEOGRAPHY. 



The outer or coastal lowland is a smooth plain, with open 
pine woods or grassy savannahs ; this division is about 50 
miles wide, rising inland 2 or 3 feet to a mile. Its level 
surface is very poorly drained. 

Further inland the plain slowly rises with gently rolling 
surface ; here the soil is better than in the first belt, and 
much cotton is raised. Further inland still, the surface 
becomes more sandy again and more hilly, giving extensive 
views seaward across the lower plain. A hundred miles 
inland a belt of hilly uplands stands 600 or 700 feet above 




Fig. 76. — Coastal Plain of the Carolinas. 



the sea, covered with pine forests. Here the original surface 
of the plain is almost entirely destroyed by the action of 
many streams in carving their valleys; and by the action of the 
weather in opening the valley slopes ; and this part of 
the plain may be described as " well dissected." Then come 
the hills of the older land (the Piedmont belt, here not moim- 
tainous, but of moderate relief), whence the strata of the plain 
have received their sediments, and where the rivers are now 
cutting down narrow valleys beneath their former valley 
floors. 



PLAINS AND PLATEAUS. 125 

The soil belts on this plain exert an important control over 
the industries of the inhabitants. The less sandy soils are 
occupied by cotton plantations ; the more sandy belts are 
covered with extensive pine forests, furnishing much lumber 
and a great amount of tar and turpentine. The moist swampy 
soils near the coast are well adapted to the cultivation of rice. 
The more limy parts of certain strata are dug up to fertilize 
the more sandy fields, and the richest of these limy deposits 
are exported to other states to be used as fertilizers. 

The strata of the plain are generally of too loose a texture 
to supply good building stone or material for making hard 
roads ; the time that has passed since the strata were de- 
posited has not been sufficient for their consolidation. There 
are no metalliferous ores, and mining is unknown on plains 
of this kind. 

The rivers that are extended from the older land have 
incised their valleys 400 or 500 feet in the inner part of 
the plain, so that they cannot cut down closer to base- 
level without losing the velocity they need in order to 
carry along their load of waste. Their branches have 
dissected the upland for several miles on each side, chang- 
ing the original surface of the plain into an irregular and 
hilly form. 

Passing seaward the valleys become shallower, and the 
uplands are less and less dissected. The rivers have developed 
serpentine or meandering courses on the marshy valley floors. 
Columbia lies on Congaree river, where it passes from the 
older land to the dissected plain. Charleston and other ports 
lie at the edge of the coastal lowland, on the widened courses 
of certain rivers where the tide comes in from the sea. The 
outer coastal plain is so even that its railroads run long 
stretches without a curve. 

In North Carolinia numerous farms on the coa,stal plain 
furnish vegetables for the markets of northern cities. The 



126 



PHYSICAL GEOGRAPHY. 



lower part of the plain is so level that extensive swamps form 
upon it ; for vegetation here hinders the run-off of the rain- 
fall, and in course of time a deep boggy or peaty deposit has 
accumulated. Water-loving trees, like the cypress and tupelo, 
form the forest cover, delaying evaporation, and thus favor- 
ing the swampy growth beneath. Here the forces that tend 




Fig. 77. — North Carolina Truck Farm. 



to wear down the land are so weak that they are overcome 
by plant growth, and the land is built up. Artificial ditches 
and canals may lead away the water, and some of the swamp 
land has been farmed after clearing off the trees. 



Artesian Wells. — Towns and cities near the shore line 
of coastal plains frequently secure a good water supply by 
sinking deep wells until a sandy layer between clayey 
layers is reached 500 or 1000 feet below the surface. 
The same sandy layer comes to the surface of the plain 
many miles inland, where the land "is several hundred 
feet higher than at the shore line. There much of the 



PLAINS AND PLATE AITS. 127 

rainfall soaks into the sandy soil, and slowly follows 
the descent of the open-textured sandy layer between the 
close-textured clayey layers. When tapped by a deep 
well, the water rises from the sandy layer, and may even 
flow forth at the surface like a fountain ; for the level of 
its discharge is much lower than that of its supply. Wells 
of this kind are called artesian wells. 

In Fig. 78, the layers reached by the wells lead ground 
water from the inner part of the coastal plain toward the 
ocean. The other layers are of close texture and contain 
very little ground water. 




Fig. 78. — Artesian Well. 

Public health is promoted by the use of artesian well water, 
which is much purer than the water of shallow wells on low 
coastal plains. Numerous artesian wells are sunk on the 
outer part of the Atlantic coastal plain of the United States. 
Even the off-shore sand reefs may gain a supply of fresh water 
from deep wells, as at Atlantic City, N. J. 

The Pall-Line. — A large river whose course is extended 
across a coastal plain often has a well-defined head of 
navigation at low falls or rapids near the inner margin of 
the plain. The falls occur where the entrenched river 
passes from a steeper slope on the resistant rocks of the 
older land to a nearly level channel excavated in the weak 
strata of the plain. 



128 



PHYSICAL GEOGRAPHY. 



This may be accounted for as follows : BC (Fig. 79) was 
the level of the sea while the strata of the coastal plain, 
FBG, were accumulating on the submarine extension of the 
old land, BG. Before the plain was uplifted, the larger 
rivers had cut valleys of gentle slope, AB, leading to the 
baselevel, B, at the shore line of that time. To-day DE is 
baselevel. The larger river has already cut a nearly level 




Fig. 79. — Diagram of the Fall-Line. 

channel, HJ, in the weak strata of the plain, but has only 
deepened its channel from AB to LNH in the harder old-land 
rocks. As long as NH\% steep enough to make falls or rapids, 
H is the head of navigation ; and a line joining such points 
on successive larger rivers is called the fall-line. 

In coastal plains of considerable breadth settlements 
near the mouth and at the head of navigation on the 
larger rivers often develop into important cities. The 
lower city is the seaport of the region. The upper city 
bears closer relation to local industries and traffic; it lies 
in the midst of a diversified region, with strong water 
power for manufacturing the varied products of rock and 
soil. 

The fall-line along the inner margin of the Atlantic coastal 
plain of the United States is marked by important cities on 
nearly every large river that crosses it. Trenton, Phila- 
delphia (at the falls of the Schuylkill), Richmond, Raleigh, 



PLAINS AND PLATEAUS. 



129 



Camden, Columbia, and Augusta are all thus located. The 
deep and narrow valleys of these rivers in the older land are 
also conspicuous results of the elevation of the coastal plain. 

Embayed Coastal Plains. — The region here figured does 
not at first sight seem to belong to the family of coastal 
plains. Long shallow arms of the sea enter between low 
hilly arms of the land. Large rivers from the back coun- 
try enter the heads of the long bays ; small streams from 
every little valley between the hills of the land arms enter 
little bays or coves on the sides of the larger bays. 

The bay heads are occupied by marshy deltas ; the land 
heads between the bays are nipped off in low cliffs showing 
layers of sand and clay. The outer ends of the land 




Fig. 80. — Embayed Coastal Plain. 

arms, fronting the open ocean, are more or less cut off. 
Sand reefs are stretched in even line, connecting the outer 
headlands so that the sea has now access to some of the 
bays only by narrow tidal inlets ; but the broader bays may 
still be open to the ocean. 



130 PHYSICAL GEOGRAPHY. 

This region, represents a. coastal plain whicli has been 
partly sunk or " drowned " beneath the sea. Before drown- 
ing, the valleys had been widely opened, and the plains 
between them had been reduced to strips of hills. Now 
the outer coastal lowland and the broad valley floors are 
under water, the latter being occupied by the bays that 
enter far toward the old land, while the hill strips stand 
forth as ragged arms of the land. The former simple shore 
line is thus exchanged for a very irregular shore line. 

The relative change in the attitude of land and sea is here 
opposite to that inferred in the previous examples. Since the 
depression of the region, the land heads have been more or 
less cut back by the waves, and the bay heads have been 
somewhat hlled by marshy deltas. But the drowning cannot 
have taken place long ago, as the earth counts time, for the 
changes in the land heads and bay heads are of moderate 
amount. Although at first not seeming to be related to other 
examples of this series, this irregular land form is now seen 
to be little removed from them. 

The Atlantic coastal plain from Delaware bay to Pam- 
lico sound presents many examples that fall under this 
class. They are best seen about Chesapeake bay and the 
lower Potomac, where the relief is stronger and the bays 
are longer than further north and south. The outer shore 
line is for the greater distance a smooth sand reef enclosing 
a lagoon ; but at a few points the reef is exchanged for a 
low bluff cut in an arm of the mainland, as in the south- 
east corners of Delaware and Virginia. Low cliffs have 
been cut in the little land heads and small marshes have 
been formed in the little bay heads of the inner shore 
line. 



PLAINS AND PLATEAUS. 



131 



Partly drowned coastal plains exert a peculiar control over 
the distribution and occupation of their population. The 
greater part of the valley lowlands is lost, and the people 
must make the most of the hilly land arms that remain above 
sea level. The axis of each of the larger arms is generally 
followed by a main road, making its way from village to 
village among the upland farms, and giving forth side roads 
to the smaller land arms or to the little bay heads. 

Villages are found on the more level parts of the upland 
and on the better harbors of the bays. The shallow bays arc 




Fig. 81. — A Branch of Chesapeake Bay, Maryland. 

valuable for fishing grounds. More important centers of 
population are found either near the heads of the larger bays, 
where the large rivers come out from the back country and 
reach tide water, or near the mouths of the bays where the 
sand reefs are not continuous and the ocean is easily reached. 
Baltimore and Norfolk are good examples of cities thus situ- 
ated. The outer shore line is inhospitable ; its long sand 
reef offers no landing place ; and the narrow tidal iiilets allow 
entrance only to small-sized vessels. 

In the early history of " tide-water Virginia," the numerous 
drowned valleys afforded easier communication between the 



132 



PHYSICAL GEOGRAPHY. 



settlements than was found overland through the forests of 
the coastal plain. 

The interesting question of the origin of the forces suf- 
ficient to deform the crust of the earth and to elevate or 
depress a coastal plain cannot be well explained in the present 
state of science. It is important that the student of physical 
geography should recognize the facts of elevation and depres- 
sion, and should understand the importance of such movements 
in controlling the forms of the lands and in determining the 
conditions of their inhabitants ; but the processes that cause 
such movements must be left to the more advanced study of 
geology. 

Belted Coastal Plains. — Fig. 82 exhibits a district lying 
between a hilly inner land and a new shore line,. in which 
the strata have the same seaward slope that prevails in all 




Fig. 82. — A Belted Coastal Plain. 



coastal plains, but in which the form is novel. The district 
may be divided into three longitudinal belts, each one 10, 
20, or more miles wide ; the innermost (A) is a lowland of 



PLAINS AND PLATEAUS. 133 

weak strata and fine deep soils ; tlie middle belt (B) is an 
upland of firmer strata and thinner soils, several hundred 
feet above the lowland; the outer belt (6^) is a smooth coastal 
lowland. The several belts recall the belt-like arrange- 
ment of soils described in the case of a broad coastal plain, 
but this example is peculiar in having the middle belt 
occupied by an upland that runs about parallel to the shore 
line and stands between an inner and an outer lowland. 
The upland descends by a rather steep slope facing inward 
to the inner lowland, and by a long, gentle, outlooking 
slope to the coastal lowland.^ 

The reason for this arrangement of upland and lowland is 
that the undermost layers of the coastal plain are weaker than 
the middle layers ; hence the under layers, which reach the 
surface of the plain near its inner border, are already worn 
down to a lowland, while the more resistant middle layers 
preserve an upland height. 

The drainage of a belted coastal plain possesses some 
peculiar features. The larger rivers, extended from the 
inner hills, still run directly to the sea, passing across the 
inner lowland in shallow open valleys, and trenching 
through the upland belt in deep narrow valleys. Smaller 
streams are extended from the older land to the inner 
lowland, there turning to the right or left and forming 
longitudinal streams that run about parallel to the upland 
belt until they reach a large transverse river. The longi- 
tudinal streams are also joined by short streams that flow 
down ravines in the in-facing slope of the upland belt. 

1 An upland of this kind may be called, a cuesta, following a name of 
Spanish origin used in New Mexico for low ridges of steep descent on one 
side and gentle slope on the other. 



134 



PHYSICAL GEOGRAPHY. 



When these arrangements of form, soil, and drainage are 
well marked, the distribution and occupations of the people 
become closely sympathetic with them. The outer coastal 
lowland has its fishermen and sailors, with ports at the river 
mouths and villages on the smaller streams ; it also has 
interests in pastures, forests, and farms. 

The inner lowland is generally an agricultural district, 
often of great fertility. It provides a longitudinal inland 
pathway of even surf ace, often followed by highways and rail- 
roads. The junction of longitudinal streams with a large 
transverse river makes an attractive place for settlement; it 

has convenient relations with 
the old land and the inner low- 
land, with the advantage of open 
passage to the sea. Water power 
may be furnished by rapids at 
the fall-line. 

The upland belt is more sparsely 
populated ; its thinner soils may 
hardly repay cultivation, and 
much of it may remain forested. 

The coastal plain of Ala- 
bama (Fig. 83), part of the ex- 
tension of the Atlantic coastal 
plain around the border of the 
Gulf of Mexico, possesses an 
upland belt and an inner low- 
land. The older land is the 
southern end of the Appalachian mountains, here of no 
great height ; it is a region of resistant rocks containing 
iron ore and coal beds, which support the important indus- 
tries of mining, smelting, and manufacturing. The strata 
of the coastal plain are generally still of loose texture, 




ULF OF M E X J a O'^^-^^ c^ 



Fig. S3. — The Coastal Plain of Alabama. 



Plains and plateaus. 



135 



those of the upland belt behig the firmest. They contain 
marine fossils, some of the strata being largely composed 
of shells. 

The inner lowland is worn down so smooth and level that 
the rainfall is drained slowly from its surface; the roads are 
nearly impassable in wet weather. It is called the " Black 
prairie " from tlie dark 
color of its rich £ i 
weathered from the w( 1 
underlying limestoi 
This belt includes i i 
best cotton district of ^ Ii 
state, the cities of Mem 
gomeiy and Selma k 
withm it r , ^ 1 i>* S- «S '« 

The upland, local' ';^^y, j,^^, ifj .'l^^' ')l^x.]l^ 
known as the Chun t- /^''Milivl- V''^- r flu #1 



"I • - 





■*'-»wV 




Fig. 84. — Pine Forest on Coastal Plain, Alabama. 

nugga ridge, ascends rather abruptly 200 feet above the low- 
land ; it is upheld by a stratum of more resistant limestone. 
I^umerous short streams run down the infacing slope to the 
inner lowland, wearing short valleys and fringing the inner 
margin of the upland with hills. The '' hill prairies " lie on 
the broad upland surface. 



136 



PHYSICAL GEOGRAPHY. 



The outer slope descends gradually to tlie " coastal prairies," 
the surface being dissected by small streams in shallow valleys. 
Extensive pine forests occur here as well as on the upland. 
Mobile, an important port of the Gulf coast east of the Mis- 
sissippi, lies on the slightly drowned lower course of the 
united rivers of the region. 

Ancient Coastal Plains. — In Wisconsin, far inland from 
the ocean, the northern part of the state is occupied by 

rugged highlands 
of resistant rocks. 
Adjoining on the 
south and east are 
jDlains and uplands 
arranged in belts, 
their rock layers 
sloping gently 
away from the 
highlands and lap- 
ping on one an- 
other like great 
shingles. 

Fragments of the 
highland rocks are 
found in the lower members of the overlapping strata ; numer- 
ous marine fossils, like corals and shellfish, occur in many 
layers. All the layers are well consolidated; the firmer ones 
form the uplands, with distinct infacing slope and very gentle 
outward descent ; the weaker layers underlie the plains. 

Although the sea may now be a thousand miles away, the 
belts of upland and plain are easily seen to be similar to the 
belted coastal plains already described, while the rugged high- 
lands stand in the relation of the older land from which the 
strata of the plains and uplands were long ago derived. 




Fig. 85. — Ancient Coastal Plain of Wisconsin. 



PLAINS AND PLATEAUS. 137 

Tlie strata here observed are generally so well cemented 
that they must be much more ancient than those of the earlier 
examples ; a long period in the earth's history is needed for 
infiltering waters to bind together sediments grain by grain. 
Some of the strata are crossed by fissures containing lead ore 
in quantities sufiS-cient for profitable mining. This also sug- 
gests great age ; for a vast duration of time is necessary to 
gather the minerals of the ore from the surrounding strata 
through which they were originally scattered, and to concen- 
trate them i^ fissures by the action of slowly infiltering waters. 
The seashore is now a great distance away, and this also 
implies a long time during which the continent has grown to 
its present dimensions by repeated uplifts. 

In view of all this it must be concluded that this is not 
a modern but an ancient coastal plain ; that is, a region 
that began its history as a coastal plain ages ago in the 
earth's history, and that has since then been built into the 
interior of the continent by successive uplifts and addi- 
tions to the margin of the growing continental area. The 
upper layers of the original coastal plain have been greatl}^ 
worn away, and a considerable part of the highland border 
is stripped of the strata that once lapped over it. 

Artesian wells are as important a source of water supply on 
ancient as on modern coastal plains. Many such wells have 
been bored in southern Wisconsin. 

In passing southward from Canada to western Pennsylvania 
one crosses an ancient coastal plain with its strata dipping 
gently southward, and bearing various signs of early origin. 
The highlands of Canada are the older land. Next comes an 
inner lowland, the Ontario lowland plain, in part occupied by 
Lake Ontario. Then follows the Niagara upland belt formed 
on the firm limestone beds of that name, and famous for the 
gorge cut by the great cataract. A second lowland, the Erie 
lowland plain, stands a little higher than the first, partly 



138 



PHYSICAL GEOGBAPHY. 



occupied by Lake Erie ; and finally conies a rather strong 
infacing slope ascending to a dissected uj)land, the northern 
part of the Allegheny plateau. 

The Niagara upland fades eastward as its limestone layer 
thins out, and is not seen beyond Rochester, where the 
Ontario and the Erie lowlands come together. The Allegheny 

plateau weakens west- 
ward, and is not trace- 
able beyond Cleve- 
land. Eastward it 
becomes stronger; 
the irregular infacing 
slope is much dis- 
sected by valleys, and 
frequently consists of 
several successive 
benches. It extends 
to the bold Helder- 
berg escarpment 
southwest of Albany 

Fig. 86. — Ancient Coastal Plain of Ontario and New York. (SCC -tig. vZ), WJiere 

the Adirondacks rep- 
resent the older land and the Mohawk valley is the narrow 
inner lowland. 

The rugged highlands of Canada and the Adirondacks are 
heavily forested. The Allegheny plateau is so hilly that its 
population is relatively small. The Ontario and Erie plains, 
where not drowned by their lakes, contain a thriving popula- 
tion. The Mohawk valley in particular has long served as a 
path of travel and transportation. The Erie Canal connects 
the tidal Hudson with Lake Erie. Important railroads follow 
the same course. The southern part of the lowland has thus 
come to be the seat of many cities in a rich agricultural popu- 
lation. Albany, Schenectady, Utica, Syra-cuse, Auburn, Roches- 
ter, Buffalo, Erie, and Cleveland all lie on the plain near the 
border of the plateau. 




PLAINS AND PLATEAUS. 



139 



A beautiful example of an ancient coastal plain is found in 
England. Its successive features are encountered while pass- 
ing from the older land of Wales to London and down the 
Thames to the North Sea. They are roughly shown in Fig. 87, 
where the heights are much exaggerated. Here, curiously 
enough, the mountainous older land (A) lies next to the 
Atlantic, and the coastal plain slopes toward the continent of 
Europe. The plain no longer retains anything of its original 
surface, unless in parts of eastern England, where the latest 



^^^^^ft 




^^^ 


c 


D 




.___£;_^ 


^?S^l^efe§vS^^^ 


■ 




M 


R 


Hi 



Fig. 87. — Diagram of Ancient Coastal Plain of Middle England. 

elevation has added a young coastal lowland (F) to the former 
land area. Nearer the older land there are two well-defined 
upland belts, the Cotswold (C) and Chiltern (E) hills; and 
two lowlands, those of Worcester (B) and Oxford (D). All 
these features have a considerable extension to the northeast 
and southwest, with varying strength and expression. 

Inland Plains and Plateaus. — The relation of certain 
regions, composed of nearly horizontal rock layers, to an 
older land is not so simple as in the plains thus far 
described. Several examples of this kind will be given 
in which the older land need not be considered. 



Young Plains The great plain of western Siberia, in 

latitude 60° to 60° N., stands at a moderate altitude above 



140 PHYSICAL GEOGRAPHY. 

sea level, and preserves an even surface over hundreds of 
miles. Vast areas, stretching further than the eye can 
reach, are monotonous in the extreme, almost as uniform 
in soil as in surface. The flat areas between the streams 
are as yet practically undivided among the rivers, having 
no distinct lines of water parting and no distinct channels 
of water discharge. Marshes, alternately wet and dry in 
winter and summer, and many shallow lakes lie in faint 
depressions ; as if slight inequalities in the original sur- 
face of the plain had not yet been drained by river action. 
The valleys are few and far between; they can never be 
cut deep while the region stands low. They are narrow; 
hence the rivers have as yet worked only for a compara- 
tively short time in the earth's history. The plains are 
still young. 

The more northern part of the central plains is forested ; 
but about latitude 50° to 55° the plains have a lighter rainfall 
and are treeless ; clothed with thin grass in summer ; cold, 
barren, and wind-swept in winter. Taken with similar low 
plains further north and south, the vast area from the Caspian 
Sea to the Arctic differs much less in form than in climate ; 
they are frozen in the north, parched in the south, temperate 
in the middle. 

The plains have long been the home of wandering tribes, 
whose wealth is not in fixed possessions, but in herds and 
flocks driven from place to place for pasture. The people live 
in tents, and move about without definite limits to their lands. 
Every man is necessarily a horseman, competent in nearly all 
the arts of a wandering life. The horse, descended from a 
long line of prehistoric ancestors on open plains, has lost the 
lateral movement of the limbs that climbing and flesh-eating 
animals possess, but has at the same time gained in speed and 
endurance, thus becoming the mainstay of wandering tribes. 



PLAINS AND PLATEAUS. 



141 



Young Plateaus. — Fig. 88 represents part of an exten- 
sive upland or plateau that is traversed by deep and narrow 
valleys or canyons branching in various directions. The 
plateau is built of horizontal rock layers of various kinds, 
well shown in the canyon walls. The broad upland has a 
comparatively even surface, often so monotonous that it 
receives less attention from explorers than the canyons 
that dissect it. The irregular course of the canyons indi- 




Fig. 88. —A Plateau in Arizona. 

cates that the rivers which cut them had no well-defined 
slope on the original upland to guide their flow. The 
irregular branching of the side canyons shows that it has 
been about as easy for the streams to wear back the head- 
water ravines in one direction as in another. 



The great altitude of the uppermost stratum, forming the 
general surface of the upland, and the depth to which the 
canyons have been worn down by the rivers prove that 
the whole region has been broadly uplifted from the sea in 
which the strata were laid down. 



142 



PHYSICAL GEOGRAPHY. 



In regions of this kind some of the side canyons are 
still so narrow that the stream occupies all the space at 
the base of their walls ; it flows mostly on bare rock with 
rapid descent. Such a stream is deepening its valley by 
grinding the rock bed with the fragments of rock waste 
that it washes down. Other valleys are somewhat broader, 
part of their floor being occupied by narrow strips of 




Fig. 89. — Diagram of Narrow Canyon. 



flood plain, overflowed by the river at the time of high 
water. Here the river has almost ceased to deepen the 
valley; the slope of its channel just gives it velocity 
enough to wash along, the waste that is weathered from 
the valley walls and worn from the side canj^ons. 

Although a great deal of work has been done in cutting 
down and widening these canyons, it is manifest that a 
vastly greater work still remains to be done before the 
broad mass of the plateau is worn down close to base- 
level ; hence a plateau of this kind must be called young, 
however deep its canyons may be. 



PLAINS AND PLATEAUS. 



143 



In the narrower canyons the descent from the plateau leads 
down over a succession of cliffs and slopes. The cliffs are 
the edges of resistant layers (b, c, d, e, Fig. 89) ; they, advance 
around every spur and turn into every side ravine, but always 
follow the level of the guiding layer. The slopes follow the 
weak layers ; they are covered with coarse rock waste, or 
talus, weathered from the cliffs above. The rock waste 
weathers and falls from each cliff", and rolls, washes, and 




Fig. 90. — Diagram of Widened Canyon, 



creeps down each slope to the top of the cliff next below, 
where it falls again; thus at last reaching the stream, where 
its finer parts are rapidly washed away. Thus the cliffs and 
slopes wear back or retreat, and the canyon widens. 

As a canyon widens, the thickest and strongest cliff-maker 
(c, Fig. 90) wears back more slowly than the thinner, less 
resistant cliff-makers. The less resistant cliffs below the 
stronger one wear back till they nearly or quite disappear 
beneath the talus, as a, h. The faster retreat of the less 
resistant upper cliff d leaves a platform or bench sloping 
gently forward from the base of the talus to the top of the 
stronger cliff c. In the same way a platform stretches for- 



144 PHYSICAL GEOGRAPHY. 

ward from the base of the talus of c to the top of the cliff d. 
Fine waste from the talus is washed forward across the plat- 
form. 

The steeper streams of young plateaus leap in rapids or 
falls where they descend across the edges of cliff-making 
strata. The streams rasp and cut back the fall-making 
strata with the waste that they carry, and the falls there- 
fore retreat up stream. In the larger rivers the falls are 
worn back and extinguished while the plateau is still 
young. In the smaller streams falls may survive until 
the plateaus are thoroughly dissected. 

Fig. 91 is a section along a stream in a plateau, in which a 
fall occurs at B. The fall will be extinguished when it is 




Fig. 91. — Diagram of a Waterfall in a Canyon. 

worn back so far up stream that the backward extension BD 
of the river bed AB intersects the top of the fall-making 
stratum JECD. 

The lofty plateaus of north Arizona, traversed by the 
Grand Canyon of the Colorado from east to west (see 
frontispiece), include many illustrations of this class of 
forms. The Sheavwits plateau, at a general altitude 
of 6000 feet, may be taken as a type example; it is cut 
across by the western part of the canyon. 

The arid climate of the plateau excludes nearly all vegeta- 
tion, and lays bare the details of structure and form. The 
region offers no temptation to settlement, however marvellous 



PLAINS AND PLATEAUS. 145 

it is to the explorer. It is naked and desolate, occupied by a 
few Sheavwits Indians, who subsist by " cultivating little 
patches of corn, gathering seeds, eating the fruits and fleshy 
stalks of cactus plants, and catching a rabbit or lizard now 
and then ; dirty, squalid, but happy, and boasting of their 
rocky land as the very Eden of the earth." 

The great elevation of this plateau permits an exceptional 
depth of canyon cutting. The massive strong and weak strata 
of which the plateau is built produce strong cliffs and long 
talus slopes on the canyon walls. Far down in the bottom of 
the great trench runs the tawny Colorado, turbid with waste 
that is showered from the walls in rocky avalanches or swept 
in from side canyons by cloud-burst torrents. 

Deep as the canyon is, it has been cut down only by the 
river. There is no indication of clefts or fractures along 
the river course. The strong rock layers in the walls weather 
more slowly in the dry climate there prevailing than they 
would in a wetter climate ; hence the plateau is advancing 
with relative slowness toward a well-dissected form. 

Unlike most great rivers, whose valleys serve as paths of 
travel, the Colorado is almost inaccessible along its canyon. 
Only one exploring party has successfully gone down the 
canyon ; their narrative is a wonderful history of scientific 
adventure. Once entering the canyon in their boats, retreat 
was impossible against the swift current. Escape by climb- 
ing the walls was hazardous. To descend the river was easy 
on its smooth stretches, even though hemmed in by great 
cliffs ; but cascades had to be passed where the most resistant 
beds are not yet cut through, and rocky rapids obstruct the 
channel where side canyons deliver heaps of boulders to 
the main river. After many perils the party came out to the 
open lower country, west of the Sheavwits plateau. 

In the young stage of dissection plateaus are, as a rule, 
occupied only on their upland surface. The elevation of 
the upland is an advantage in the torrid zone, where the 



146 PHYSICAL GEOGRAPHY. 

high temperature prevailing at sea level is willingly 
exchanged by civilized races for more moderate tempera- 
ture at altitudes of several thousand feet. But in the 
temperate zone a high plateau is at a disadvantage from 
the rigor of its winters as well as from its difficulty of 
access. 

The canyon-like valleys are obstacles to movement; 
they serve as barriers (except to birds and winged seeds) 
between the uplands on each side. They are seldom 
inhabited, unless by the people of a persecuted tribe, who 
sometimes take refuge as "cliff-dwellers" in the recesses 
or caves that are often excavated between cliff base and 
talus top. 

Even in a moist climate the bare rocky cliffs of canyon 
walls are in effect so many small deserts, almost free from 
plant and animal life. The steeper talus slopes may support 
trees and bushes ; where a little finer waste accumulates, 
smaller plants may also grow. Caves and burrows among 
loose rocks shelter many kinds of animals ; but a talus slope 
is too steep and coarse textured for higher uses. Conquered 
races, driven from wider possessions, may settle on the broader 
upland platforms or on the flood plains of the more open 
valleys ; but these surfaces are too limited in extent and, in 
plateaus of strong relief, too isolated to attract the more 
fortunate and powerful races. 

Dissected Plateaus. — The rugged u^Dlands that extend 
continuously from New York to Alabama, known as the 
Catskill, Alleghen}^ and Cumberland plateaus, may here 
be treated together under the second name. The whole 
region consists of nearly horizontal strata. The hilltop 
view generally discloses an even sky line, which may be 



PLAINS AND PLATEAUS. 



147 



taken roughl}^ to define a surface that once extended over 
the whole region, before the valleys were carved. Thus 
reconstructed, the upland surface would rise gradually 
from Ohio and western Kentucky to the east and southeast, 
reaching the greatest height 
near its eastern margin, 
where the plateau de- 
scends abruptly to 
the Appalachian 
valleys 
At pres 

e nt 
the up- 
land surface 
is thoroughly dis- 
sected by branching 
valleys. The region 
should therefore not be 
described simply as a plateau ; 
it is a dissected plateau, in an ad- 
vanced or mature stage of geographi- 
cal development. The altitude of the 
iginal upland in West Virginia (roughly 
or 3500 feet) has been great enough to 
Fig. 92. -The permit the erosion of valleys 1000 or more 
^lateau^ feet deep ; hence some of the intervening 
plateau remnants have strong relief, and fairly 
deserve the popular name of " mountains " locally applied 
to them. 

Many resistant sandstone layers stand out in cliffs, 10 to 
50 feet high, running in bands around the spurs of the great 




148 



PHYSICAL GEOGRAPHY. 



hills. The weak strata occupy the intervening slopes, covered 
with a thin stony soil, and supporting a vast forest. The hills 
and spurs are all very much alike, for they are developed 
by similar streams on similar structures. Every side valley 
resembles all its neighboring fellows ; all the members of a 
local tribe of small streams cascade down over the same number 
of fall-making strata on their descent to the larger rivers. 

In contrast to the previous example, this district has nearly 
everywhere lost its once continuous upland surface, and is 




rig. 93. — Canyon of Kanawha River in Allegheny Plateau, West Virginia. 



now transformed into a hill-and- valley country. There are 
many small cliffs instead of a few great ones ; hence platforms 
are seldom developed to notable breadth. A great part of the 
surface consists of hillside slopes. Drainage is not delayed 
on extensive uplands, as in young plateaus ; but at times of 
rain or late winter thaws, water is quickly shed from the hills, 
and the main streams rise rapidly in destructive floods. 

The forests retard but do not prevent the wash of waste 
from the steep slopes ; denudation is actively advancing, and 
the load of waste delivered to the rivers is greater than in the 
youth of the region, when the upland was less dissected. 



PLAINS AND PLATEAUS. 149 

As a whole, the Allegheny plateau is so rugged that its 
population is small, being generally found on isolated 
farms upon the disconnected uplands, in villages and occa- 
sional small cities in the valleys, or gathered about mines 
or other industrial works. The isolated hilltop farmers 
cannot afford to construct and maintain good hillside 
roads; it is difficult to haul upland products down bad 
roads to village markets or to railroad stations; and it is 
doubly difficult to haul supplies up to the farms. Life on 
the uplands is laborious. 

The hillsides are generally too steep for cultivation ; if 
cleared, the soil is rapidly washed away. Wild animals, 
such as deer and bear, long ago exterminated from the lower 
country on the east and west, still find refuge here ; small 
game is abundant, and hunting is almost as much of an occu- 
pation to the " mountaineers " as farming. 

The forests supply lumber to the more thickly settled com- 
munities on the east and west. The numerous coal seams 
(vegetable deposits in ancient marshes, now members of the 
great series of horizontal strata that build the plateau) are 
well exposed in the deej)-cut valleys, and are now extensively 
mined. Iron ore occurs in certain strata. Eock oil and 
natural gas are found by boring deep wells. It is chiefly in 
connection with the industries dependent on these important 
products that a larger population is to-day attracted to this 
rough country. In the earlier history of the United States 
the dissected plateau was (excepting the North Carolina 
mountains) the most formidable barrier between the Atlantic 
coastal plain and the open prairies of the Ohio valley. 

Intercourse and traffic are still so difficult in the districts 
of stronger relief, away from the lines of travel, that the 
people are slow in acquiring the ways of civilization. Family 
feuds are still maintained among the " mountaineers " of West 
Virginia and Kentucky. As the uplands decrease in height 



150 PHYSICAL GEOGRAPHY. 

westward, and the valleys become more open toward the Ohio 
river, population increases ; but Pittsburg is a city of excep- 
tional size in this region. Its growth in early years was 
favored by its position with reference to the lower Ohio valley, 
and in later years by the great stores of mineral wealth in the 
surrounding country. 

Parts of the Cumberland table-land have broad uplands 
holding villages, and traversed by high-level roads. A very 
rugged part of the plateau is known as the Catskill mountains, 
in eastern New York ; the higher parts are forested and unin- 
habited. The plateau here descends by a bold escarpment to 
the Hudson valley. 

Old Plateaus. — Broad plains of gently rolling surface, 
drained by streams in wide-open, flat-floored valleys, are 
sometimes surmounted by flat-topped " table-mountains." 
Neighboring tables are of nearly uniform height, each one 
being capped by a resistant cliff-making rock layer and 
flanked by a sloping talus ; they differ chiefly in area and 
outline. In the western United States tables of moderate 
height are often given the Spanish name mesa (= table ; 
pronounced may-sa) ; while the smaller mesas are known 
by the French name butte (= target or landmark ; pro- 
nounced bewt). 

Mesas and buttes of this kind are the scattered rem- 
nants of strata that once spread far and wide over the 
region, forming an extensive plateau. The original surface 
of the plateau may have been much higher than the tops 
of the mesas ; for the uppermost strata may now be com- 
pletely swept away. The valleys have widened so greatly 
that their floors occupy a great part of the surface. A 
region of this kind represents an approach to the old age 
of a plateau. 



PLAINS AND PLATEAUS. 



151 



The plains of western New Mexico are surmounted by 
numerous remnant mesas. Settlement here is chiefly limited 
to the lower lands. The isolated mesas and buttes, risinsr 
several hundred feet over the plain, are generally unin- 
habited ; thus the old age of a plateau reverses the conditions 
of its youth, in which the uplands alone could be easily 
occupied. 

The mesas of an old plateau are not, like the canyons of 
a young plateau, obstacles to travel ; for while can^^ons are 
continuous for long distances and are everywhere difficult to 
cross, mesas are discontinuous, and many broad passages are 
opened among them. They are occasionally occupied as 
natural citadels by barbarous tribes. 

One of the most remarkable remnants of an old plateau 
is the so-called Enchanted Mesa of western New Mexico. 




Fig. 94. — The Enchanted Mesa, New Mexico. 



It rises more than 400 feet above the surrounding plain, 
and although no longer inhabited, it was once occupied 
by a tribe of Indians, who found safety on its almost 
inaccessible summit. 

Other mesas in New Mexico and Arizona are still occupied 
by small tribes of Indians, whose compact groups of houses 



152 PHYSICAL GEOGRAPHY. 

on the upland cannot, at a little distance, be distinguished 
from the rock walls of the cliffs. They cultivate small patches 
of corn on the lower ground, but do not venture to build settle- 
ments there for fear of attack from more warlike tribes. 

In the interior of British Guiana gigantic remnants of an 
old plateau rise over the surrounding lower country. Huge 
mesas are rimmed round by almost inaccessible cliffs that 
stand above long talus slopes. One of the highest is Eoraima, 
whose broad table is more than 2000 feet above its base. It 
is uninhabited, and until recently had never been ascended. 
The natives of the forested wilderness around it believe that 
the upland is occupied by spirits. 

Old Plains. — It may be imagined that, at a very late 
stage of development, even tlie mesas and buttes of an 
old plateau may be worn away, the whole region being 
then reduced to a gently rolling lowland, a worn-down 
plain, or " plain of denudation." ^ Many examples of this 
kind are known, but most of them have been again 
elevated, and are now undergoing a new series of changes. 

Central Russia is a nearly level region of moderate 
altitude. It is one of the largest known examples of a 
worn-down plain. At first sight it might be mistaken 
for a young plain, so nearly even is the greater part of its 
surface ; but a closer examination reveals many features 
that do not correspond with those of young plains. The 
subsoil rocks still lie in almost horizontal layers, but they 
do not consist of loose sands and clays. Many of them 
have a rather firm texture, showing that they have existed 
long enough to have their particles bound together by the 
very slow action of infiltering waters. 

1 A lowland of this kind may be called a "peneplain," because it is 
an " almost plain " surface. 



PLAINS AND PLATEAUS. 153 

Besides this, the surface of the plain does not agree with 
the surface of the uppermost rock layer, as is the case 
in young plains, but bevels across the nearly horizontal 
layers at a faint angle, so that in passing from place to 
place, different layers are exposed, causing advantageous 
changes of soil and slight variations of form. 

A region of this kind must have once had a much higher 
surface ; it may have been high enough to deserve the name 
plateau. As time passed, rivers must have at first cut narrow 
valleys across it. Then many branching valleys must have 
been carved among numerous hills, like those of West Virginia 
to-day. Finally, the valleys became broader and broader by the 
wasting of their sides, and even the remnant mesas and buttes 
were worn away. The plateau must have then been a broad 
lowland, on whose surface the rivers could cut down no deeper. 

Yet to-day the rivers of central Russia flow in rather narrow 
valleys of moderate depth. Hence it must be supposed that, 
after the ancient plateau was worn down to a low plain, the 
whole region was broadly uplifted, and thus the rivers 
regained the power of carving valleys. In the present series 
of changes the dissection of the plain has not advanced much 
further than that of the young plains of western Siberia. 
Like these, the Russian plains have a vast extent north and 
south. The difference of climate between the northern and 
southern parts, due to the globular form of the earth, exerts 
a great control on their fitness for occupation. They are 
frozen and barren in the north, where they are overlapped by 
younger plains that slope to the Arctic shore ; here the popu- 
lation is scanty. They are dry and barren in the southeast, 
where they are overlapped by the young plains of southwestern 
Siberia ; here wandering tribes drive their flocks from place 
to place. The middle and next southern parts are the most 
fertile and here a great agricultural and commercial population 
is gathered in villages and cities, 



164 PHYSICAL GEOGRAPHY. 

The greater part of Missouri is a worn-down plain, now 
uplifted and again dissected. It is an agricultural district, 
the broad uplands generally being occupied in preference 
to the narrow valleys. The strata of the region are 
gently arched, and their highest part is known as the Ozark 




Fig. 95. — The Ozark Plateau, Missouri. 



plateau. The sky line of the uplands represents the low- 
land plain that was formed at the close of the previous 
series of geographical changes. The valleys have been 
carved since the region was again uplifted. 



c d 




Fig. 96. — Section of the Ozark Plateau. 



The weaker layers (d, d, Fig. 96) have been broadly etched 
out beneath the uplifted level (p, p) of the region. The 
uplands (c, c) resemble the upland belts of belted coastal 
plains in having a steep front, made very ragged by the dis- 
section of many short but rapid streams ; a broad top, much 



PLAINS AND PLATEAUS. 



155 



broken by narrow valleys ; and a long sloping back. The 
height of the uplands over the lower lands is from 100 to 300 
feet ; their height above sea level reaches 1500 or more feet. 

A similar description might be given to a large part of the 
basin of the Ohio river. It is a region of moderate relief, 
with the advantages of good soil and sufficient rainfall. 
Hardly more than a wilderness at the time of the Kevolution 
(1776), it is now occupied by a great agricultural population, 
dotted here and there with large and growing cities, and 
crossed in all directions by railroads. 

Broken Plateaus. — The plateaus of northern Arizona, of 
which the Sheavwits already described is one, stand in a 
curious relation to one another. East of the Sheavwits 




Fig. 97. —Broken Plateaus. 



comes the Uinkaret, presenting the same upland (diver- 
sified by volcanic cones and lava flows), and exposing the 
same succession of cliffs and talus slopes in the canyon 
walls; but the Uinkaret stands about 1800 feet higher 



156 



PHYSICAL GEOGRAPHY. 



than the Sheavwits. The two are separated by a high and 
ragged cliff or escarpment, known as Hurricane ledge, 
facing westward. 

Tracing this cliff to the canyon, it is found to stand on 
the line of a great north and south fracture, which divides 
the whole mass of strata into two blocks; the eastern 
block (Uinkaret) being lifted nearly 2000 feet higher than 

the western (Sheavwits). 
This is easily proved by 
the displacement of the 
various cliff-making 
strata in the canyon 
wall. Several other 
similar plateau blocks 
are found in this region. 

The western boundary 
of the Sheavwits plateau 
{A, Fig. 98) is another 
ragged west-facing cliff, 
2000 or 3000 feet high, 
and so bold that it pro- 
vokes rainfall from winds 
that must rise as they 
pass over it. Settlers on the lower arid land use the 
streams that descend from the gigantic ravines in the cliff 
face to irrigate their ranches. Great volumes of rock waste 
have been washed down from this bold escarpment upon the 
lower land, to which the name of " Grand Wash " is therefore 
given ; and the ragged bluffs of the escarpment are called the 
Grand Wash cliffs. The Colorado river, coming out from the 
canyon in the Sheavwits plateau to the lower land on the west, 
follows a more ordinary valley of moderate depth and open 
slope ; some of the same rock layers that cap the plateau are 




Fig. 98. —Diagram of Blocked Plateaus. 



PLAINS AND PLATEAUS. 



157 



here seen low down along the river bank. Where the river 
cuts the base of the Grand Wash cliffs, the fracture by which 
the upper and lower blocks are displaced may be discovered 
on the valley sides. 

East of the Uinkaret (JB, Fig. 98) come several other 
plateau blocks. The barren surface and varied form and 
colors of the successive strata make the great fractures 
between the several blocks plainly apparent to the observer 
who looks from the brink of the canyon to its opposite wall. 
The Kaibab (D) is so high (8000-9000 feet) that, unlike the 
arid and barren plateaus on each side, its climate is moist ; 
it has forests, park-like groves, and grassy glades well stocked 
with game. The, canyon here has its greatest depth, cutting 
down 6000 feet through the whole series of stratified rocks 
into the foundation rocks of buried old-land at the bottom. 

The ragged cliffs, by which the ascent is made from one 
plateau to its highest neighbor, are features of a new 




Fig. 99. — Hurricane Ledge — a Fault Cliff. 



class. They are to-day undergoing active weathering and 
wasting. In the past they were less ragged than now. 
The fractures between the blocks are commonly known 



158 PHYSICAL GEOGRAPHY. 

under the name of faults ; hence the term fault cliffs may 
here be used. It is probable that the displacement or 
faulting was gradual, and that the cliffs were somewhat 
weathered even during the time of faulting. To-day they 
may be called dissected fault cliffs. 

It is truly remarkable how little attention the streams of 
this region pay to the profound fractures by which the plateau 
blocks are divided. The Grand Canyon, the most fissure- 
like of all great river valleys, pursues its course entirely 
regardless of the fissures that run across it. On the surface 
of the plateaus the fissures are evident in the fault cliffs, now 
somewhat weathered back from their original faces ; but they 
are not followed by canyons. 

The origin of the irresistible forces by which the plateau 
blocks have been broken apart and uplifted is little under- 
stood. It is undeniable that movements of uplift and dis- 
placement have really occurred, producing great geographical 
features in the wonderful plateau country of Arizona and 
Utah, but the cause of the movements is an unsolved prob- 
lem, worthy of attention from the advanced student of 
geology. 

The great plateau blocks of Arizona are set apart by their 
generally dry climate, great altitude, and deep dissection from 
the easily habitable parts of the world. Where their surface 
is most rugged and inaccessible, unsubdued tribes of Indians 
still preserve their savage ways, living in a most- primitive 
fashion on isolated plateaus surrounded and trenched by 
branching canyons. Travelling over the less dissected plateaus 
is feasible with a proper outfit of horses and provisions and 
with a good guide ; and no part of the world would better 
repay a visit by a lover of the marvellous in nature than the 
lofty Kaibab, where it is trenched by the mile-deep canyon. 



CHAPTER VII. 

MOUNTAINS. 

The Inspiration of Mountain Scenery. — Most of the peo- 
ple of the world live on lands of moderate relief, where an 




Fig 100 —The Himalaya Moontalna 



abundant soil supplies the needs of agriculture, and where 
travel and traffic are little obstructed. Rugged regions 
repel rather than attract inhabitants. The people who 



160 PHYSICAL GEOGRAPHY. 

live on lowlands liave, until modern times, usually looked 
upon high mountains as places of danger. It has been 
imagined that they were occupied by evil spirits, and that 
it must be perilous to cross their high passes or to climb 
their snow-clad peaks. Uncivilized people living in the 
valleys among mountains seldom ascend higher than to 
the pastures on the shoulders of the ridges, or to the low- 
est notches by which the ranges are broken. But in the 
eighteenth and nineteenth centuries a better understand- 
ing of nature among civilized nations has led explorers to 
press far into the deep valleys of mountains and to mount 
their lofty peaks, until now a passion for mountain climb- 
ing has arisen and many thousand travellers go every 
summer into the most mountainous country that they can 
reach, simply for the enjoyment of its scenery. 

To one who has always lived in a low country, it is a 
novel experience to climb a bold mountain slope and rise 
high above the lower ground. A wide prospect is spread 
out beneath and far away, where the hills and valleys, the 
forests and fields, the roads and streams are displayed as 
if on a map. The peaks above inspire the traveller with 
an ambition to reach their highest point and see the 
country beyond, with nothing but the sk}^ above him. A 
new sensation is aroused by the grandeur of the view from 
the summits. The massive vigor of the peaks and ridges 
excites enthusiasm, and the least imaginative observer can 
hardly fail to muse on the marvellous processes of nature 
that have brought such forms into being. The mountain 
climber who enters with sympathy into the life of the 
mountains, and who looks upon them as they, had they 
but eyes, might look on each other, gains a new under- 



MOUNTAINS. 



161 



standing of the world he lives in, a better and broader 
understanding than he had before. He may then appre- 
ciate the feeling of a guide in the Alps who once said to 
a traveller : "■ I like to be on a mountain ; one has no evil 
thoughts there." 

The Life Histoey of Mountains. 

Block Mountains: Young Stage. — In southern Oregon 
and the adjoining parts of California and Nevada there 
are many long narrow mountain ridges, extending about 




Fig. 101. — Block Mountains. 



north and south. Each ridge is a few miles wide, 10 to 
40 or more miles long, and 1000 or more feet high. 
The ridges are steep or cliff-like on one side, of gentler 
slope on the other, and are separated by flat trough-like 
depressions of varying breadth and depth. 

Each ridge consists of thick layers of rock, the surface 
of the uppermost layer forming the back slope of the 
ridge, while the cliff face breaks across the layers. The 
rock layers are similar in all the rock faces, though the 
ridges vary greatly in size. A general view of the country 



162 



PHYSICAL GEOGRAPHY. 



shows that the entire region was once a plain, but that it 
is now broken into long narrow blocks, and that the blocks 
are tilted one way and the other, so that their uplifted 
edges form the mountain crests. 




It is difficult to account for forces sufficient to break the 
earth's solid crust in this way, but, as in the plateau blocks, 
there can be no question that such forces have been at work, 

and th at they have exerted 
a great influence on geo- 
graphical conditions. 

Some of the ridges re- 
tain the form of the tilted 
blocks hardly changed by 
weathering. Their back 
slopes are smooth; their 
cliffs have little talus at 
the base. Others have 
shallow gullies worn down 
the back, while the cliffs 
are indented by ravines, 
and every ravine has a fan-like deposit of rock waste spread 
out beneath it; between the fans the cliffs have a distinct 
talus slope at their base. 

On Satas ridge in southern Washington (^, Fig. 130), great 
bodies of rock have fallen from the cliffs in huge landslides, 
so steep was the face of the uplifted block. In one case a 
landslide slipped down about 1000 feet from a cliff 2500 
feet high, leaving a scar on the cliff half a mile long, and 
plowing its way out on the plain below for nearly a mile. 
The fallen mass is much broken, having a very irregular sur- 
face. Around its margin is a rude semicircle of hills 200 
feet high, consisting of the material of the plain pushed up 
ahead of the slide. Although little weathered, the Indians 
thereabouts have no tradition of its fall. 



Fig. 102. —Mountains of Southern Oregon. 



MOUNTAINS. 163 

The tilted blocks of Oregon are, on the whole, so little 
worn that they must have been broken and tilted recently in 
the earth's history. As some of them are more gullied and 
ravined than others, the different blocks must have been 
broken at different times. Some of the fans and talus slopes 
of rock waste are slightly broken along the fracture lines at 
the base of the cliffs ; hence the breaking and tilting of the 
blocks must liave been progressive, and not all at once. The 
fractures dividing the blocks must be deep, for hot springs 
rise along their lines. 

Earthquakes are not infrequent in this region ; hence it is 
believed that the displacements are still in progress from 
time to time ; a movement of even a few inches would suffice 
to cause earth tremors, while a sudden start of a foot or more 
would produce a violent and destructive shock for many miles 
around. There is no sign that volcanic action has any con- 
nection with the fractures and earthquakes of this region. 

Here we have to do with a group of young mountains, 
whose broken attitude was given very lately in the earth's 
history. The ridges have a massive shape characteristic 
of unworn forms, not yet ornamented by the varied details 
of weathering and carving that they will gain when more 
dissected. They are less beautiful than mountains of 
greater height and more varied features, but they are of 
great interest as examples of simple geographical forms. 
Nowhere else in the world have mountains at once so 
large and so young been discovered. 

The drainage of this region is very simple, for the 
streams follow the slopes produced by the tilting of 
the mountain blocks. The smaller streams flow down the 
slopes of the ridges. The larger streams flow along the 
troughs in the direction of their slant to the deejjest 
depressions, and there form shallow lakes and marshes. 



164 PHYSICAL GEOGRAPHY. 

The finer waste from the ridges is spread evenly over the 
lower parts of the troughs, concealing their rocky floor. 

Like the rivers that are extended across young coastal 
plains, the streams of the young ridges in Oregon flow in one 
direction or another in consequence of the slopes given to the 
land surface that they drain. 

Certain features of the region depend on its arid climate. 
The rainfall is light (15 inches or less a year), for the 
lofty Cascade range on the west takes most of the moisture 
from the Pacific winds. Few of the lakes are filled to over- 
flowing ; they discharge their water supply by evaporation 
into the dry air. Most of the lakes are therefore saline, and 
the plains of fine waste about them are barren. 

In dry seasons the lakes shrink ; some of them disappear, 
leaving smooth floors of sun-baked clay. The bottom of the 
troughs elsewhere and the lower slopes of the ridges are 
clothed with bunch grass and sagebrush; the ridge slopes, 
receiving more rainfall than the lower lands, support scattered 
cedars, and the higher crests bear forests of pine and spruce. 
Had the ridges not been uplifted, the trees that now grow on 
them could not exist in this arid region. 

Although the ridges are of moderate height, they repel the 
few settlers in the region, whose ranches are all found in 
the troughs. The thin grass supports herds of cattle, and 
the streams sufiice for a little irrigation. Thus even in these 
low young ridges the effect of mountains on the climate and 
on the location of settlements is well shown. These effects 
will be found to be much more striking in mountains of 
greater height. 

Dissected Block Mountains. — In Nevada and the adjoin- 
ing parts of California and Utah there are many north- 
and-south mountain ranges, adjoined by gravelly plains 
that slope gently to flat troughs between the ranges. The 
ranges are from 20 to 80 miles long, and from 5 to 20 



MOUNTAINS. 



165 



miles wide. Their summits rise from 5000 to 7000 feet 
above the plains. They are generally steeper on one side 
than on the other ; their crests are notched and uneven ; 




Fig. 103. — A Dissected Mountain Range, TJtah. 

their slopes are diversified by well-carved spurs between 
deep valleys. Thus they possess much of the variety of 
form commonly associated with mountains. 

As compared with the ridges of southern Oregon, these 
ranges are larger and more dissected ; but the two agree in 
having a short and relatively abrupt slope on one side of the 
crest line, and a long gentler slope on the other side. 

The ranges of Nevada, like the ridges of Oregon, seem 
to have been formed by the uplifting and tilting of long 
narrow blocks, into which the region had been divided by 
profound fractures ; but in Nevada the blocks must have 
been larger and the displacements greater ; and thie break- 



166 



PHYSICAL GEOGRAPHY. 



ing and tilting must have begun earlier than in Oregon, 
for the work of dissection is here much further advanced. 
The ranges of Nevada are thoroughly or maturely dissected. 
Yet, as in Oregon, earthquakes and broken fans of rock 
waste give assurance that the mountains are still growing. 

The blocks are now so deeply carved, and their outlines 
are so irregular, that their original block form is hardly 
recognizable. With this change, the mountains have become 
much more beautiful, just as a carved statue is more beautiful 
than a rough block of marble. The rock waste, worn from 




Fig. 104. — Fractured Slopes of Kock Waste at Base of Mountain Range, Nevada. 

the valleys in the mountains, forms extensive sloping gravel 
plains in the troughs, accumulating to so great a depth as to 
rise on the flanks of the mountains and thus diminish their 
relief. 



MOUNTAINS. 167 

The strong ranges of Nevada exhibit more distinctly than 
the smaller ridges of Oregon the lower temperature, with 
greater cloudiness and rainfall, that prevails on mountains 
as compared with the plains between them. The rainfall in 
the troughs is light, but storm clouds gather round the peaks 
while the sun still shines on the plains. When the clouds 
dissolve, the mountains have been refreshed by rain or 
whitened with snow, while the plains may be as dry as 
before. 

Streams flowing from the mountains often wither away on 
the plains. Settlements in Nevada are therefore generally 
limited to a belt around the mountain base, where the streams 
may irrigate fields. Some of the ranges contain valuable 
ores ; mining towns have sprung up in their valleys. 

Old Block Mountains. — In southeastern California there 
are belts of rocky hills rising to moderate height over long 
slopes of gravelly waste, beneath which a rocky floor is some- 
times exposed in gullies. These hills are taken to be the 
dwindling remnants of mountain ranges upraised so long ago 
that now they are worn down to low relief. Their youth, in 
uncarved blocks, is long past. Even their maturity, varied 
by many ridges, spurs, and valleys, is remote. They are old 
mountains, reduced to mere hills under the patient attack of 
the weather. 

Folded Mountains : Young Stage. — The Jura mountains, 
lying along the border of France and Switzerland, consist 
of a number of parallel arch-like ranges and trough-like 
valleys trending about northeast and southwest. Each 
range consists of a series of rock layers bent upwards; 
each trough is underlaid by the same series of layers bent 
downwards. Some of the uppermost layers have been 
weathered off from the crest of the arches, while the edges 
of the harder layers remain in flanking ridges. Waste 



168 



PHYSICAL GEOGRAPHY. 



from the arches has accumulated in the troughs here and 
there, flooring them over with gravel and sand. 

The rock layers of these mountains contain marine fossils ; 
they must originally have been horizontal strata on the floor of 
an ancient sea. Since then they have been crushed into their 
arch-and-trough structure by a powerful side pressure. 

The drainage of the Jura mountains is for the most 
part like that of the Oregon ridges in following the slopes 
of the deformed surface. Short streams run down the 




Fig. 105. —Diagram of the Jura, a Folded Mountain Range. 

sides of the arches, cutting ravines on the slopes, as shown 
in the unshaded foreground of Fig. 105. Larger streams 
gather on the trough floors, and escape at one end or the 
other as opportunity offers. 

Here and there a stream cuts across an arch, wearing a 
deep gorge from one trough valley to the next, and exhibiting 



MOUNTAINS. 169 

the arched structure, as in the middle ridge of Fig. 105. The 
origin of these crosswise or transverse streams is not so 
simple as that of the others. Some of the cross gorges are 
cut where the arches are least uplifted, as if a sag in the crest 
of the arch had located the transverse stream. In other cases 
it seems as if the gorge had been cut down by its stream 
about as fast as the arch was uplifted, thus indicating a slow 
growth of the mountains. 

As in all mountains of distinct relief, the form of the sur- 
face exercises a strong control over the distribution, occupa- 
tion, and movement of the population. The valley floors are 
well settled ; villages often lie near the mouth of a transverse 
gorge. Eoads are generally limited to the lengthwise and 
crosswise valleys. By-ways and footpaths lead to the upland 
fields and pastures. Little villages are sometimes found on 
the tops of the broader arches. The steeper slopes are 
generally forested. 

ISTowhere else in the world have there been discovered 
arches and troughs of so simple a pattern and so young a 
stage as those of the Jura. The Oregon ridges and the Jura 
folds are, as it were, elementary examples of mountain forms, 
provided by nature for the better understanding of the com- 
plicated examples of structure and form in greater mountain 
ranges. 

Domed Mountains. — The Black Hills of South Dakota 
show a thick series of rock layers that have received a 
dome-like structure by the upheaval of their foundation. 
The dome is of oval outline, 100 miles north and south 
by 50 miles east and west; in area about equal to that 
of Connecticut. A great part of the covering layers has 
been weathered and worn away during and after the time 
of upheaval, and to-day the foundation rocks are exposed, 
especially in the eastern half of the dome. If built up 



170 



PHYSICAL GEOGRAPHY. 



again, the height of the dome over the surrounding plains 
would be about 6000 feet; to-day the highest summits are 
only 2000 or 3000 feet above the plains, or about 7000 
feet above sea level. 

The edges of the more resistant sandstone layers, whose 
higher part has been worn off from the dome, form ridges 
that rim around the margin of the Hills. Many streams 
have cut deep valleys leading outward in all directions 




Fig. 106. — Diagram of the Black Hills. 

from the central part of the dome, as if they had been 
guided by the original slope of the uplifted surface. 
They cut notches or water gaps in the rimming ridges. 

The rolling treeless plains surrounding the Black Hills 
have light rainfall and scanty grass. They are occupied, if 
at all, by large ranches where cattle range freely, reaching a 
stream once or twice a day. Approaching the Hills, the rim- 
ming ridges rise around them too high and steep for easy 
occupation. The valleys define lines of travel; the v/ater 
gaps in the outer ridge are of especial importance as gate- 
ways to the Hills. Next inside of the chief rimming ridge is 
a valley that has been worn down on weak layers of red clays 



MOUNTAINS. 



171 



that here and there give a bright color to its soil ; hence its 
name, the Eed valley. It is so continuous around the Hills 
that the Indians called it the '' race course." 

The central part of the dome still rises high enough to 
compel an increase of rainfall from the passing winds. The 
Hills are therefore clothed with dark forests (hence the name 
Black Hills) and support an active lumber industry. 









i 






Fig. 107. — Seadwood, a Mining Town in the Black Hills. 



The deeper valleys dissect even the foundation rocks, which 
(as is often the case in ancient rocks uncovered from a long 
burial) contain valuable deposits of gold and silver. Here 
mining flourishes and settlements grow, crowded in the narrow 
valleys. The mines need machine shops and smelting works, 
and the industries thus created demand means of transporta- 
tion. Two railroads have therefore been built from the central 
states across the open country into the Black Hills ; their 
trains resemble steamships crossing the sea-like plains to ports 
in the island-like hills. 



172 



PHYSICAL GEOGRAPHY. 



Lofty Mountains. — Lofty mountain ranges, like certain 
parts of the Rocky mountains, but better represented by 
the Alps, the Caucasus, and the Himalaya, possess a great 




Fig. 108. — Peaka of the Central Alps. 

complexity of structure and exhibit a remarkable variety 
of peaks, ridges, ravines, and valleys. Their higher central 
peaks usually consist of resistant granite-like rocks, sur- 
rounded by slanting layers of bedded rocks that rise in 
great ridges. 

These two parts once had a simple relation like that of 
"foundation " and "cover," already seen in several examples ; 
but now both the foundation rocks and the covering strata are 
greatly deformed and dissected, as if repeatedly tilted in blocks, 
uplifted in domes, and crushed in folds, and as if for a long 
time vigorously attacked by weather and streams. 

The majestic forms of lofty mountains usually depend 
as much on their deep dissection by great valleys as on 
their lofty uplift. Unlike the simple tilted blocks of 



MOUNTAINS. 



173 



Oregon, or the orderly folds of the Jura, the greater 
ranges preserve little indication of their original form. 

Lofty mountain ranges have a greater length than breadth. 
They extend in a general way parallel to the trend of their 
tilted blocks and folds, as if they represented a belt of 
country where the crust of the earth had been crushed or 
upheaved in escaping from enormous pressures from one side 
or from beneath ; but the nature of the forces which produce 
mountains is not fully understood. One of the most ingenious 
and successful theories accounts for many ranges as great 
disorderly folds formed in the outer crust of the earth, which 
is thought to wrinkle here and there as it very gradually 
settles down on the slowly cooling and contracting interior. 

The discovery of marine fossils in the bedded rocks of high 
Alpine ridges toward the close of the eighteenth century was 




Fig. 109. — An Alpine Ridge of Slanting Layers. 



received with great astonishment by the scientific men of the 
time. The occurrence of fossils in so elevated a position was 
one of the first generally accepted proofs of the changes that 



174 PHYSICAL GEOGRAPHY. 

have gone on in the past, by which the present form of the 
earth's surface has been fashioned. But not until the nine- 
teenth century had well advanced was it generally under- 
stood how much more the form of lofty mountains depends 
on processes of land sculpture than on forces of uplift. 

Peaks and Ridges. — The highest peaks and ridges of 
lofty mountains generally consist of the most resistant 
rocks. Their height is due in part to the great uplift the 
whole range has suffered, and in part to their success in 
resisting the attack of the weather, under which the 
weaker rocks have greatly wasted away. The waste that 
is shed from the peaks and higher ridges is quickly swept 
down into the valleys, usually leaving the loftiest summits 
bare and sharp. The spurs of the ridges are notched by 
steep ravines, and deep valleys are worn between them. 
Their varied form is chiefly due to elaborate carving. 

The bare rocky peaks and ridges, rising into the cold 
upper atmosphere, far above the limits of vegetation, are 
silent deserts. The stillness is broken only by the rush 
of storm winds and the roar of rockfalls and snowslides. 
Not less barren are the snow fields and the talus slopes on 
the higher mountain flanks, and the slanting reservoirs 
. of ice and snow in the upper valley heads, from which ice 
streams or glaciers slowly creep down to the lower valleys. 
The lower slopes are generally forested. 

Many summits in the Alps are so sharp that they are 
called " needles " or ''horns." They rise as almost inacces- 
sible peaks between the gnawing valley heads. Mt. Blanc, 
the highest mountain of the range (nearly 16,000 feet) is of 
dome-like form with a heavy snowcap, not yet sufficiently 
dissected by valleys to develop sharp peaks. 



MOUNTAINS. 175 

The Selkirk range of the Eocky mountains in Canada has 
steep and bare rocky summits surmounting the long waste- 
covered slopes that descend into the valleys. Having an 
abundant snowfall, the range bears extensive snow fields and 
glaciers. In the Rocky mountain ranges of Colorado the 
snowfall is less plentiful, snow fields are scarce, and glaciers 
are wanting. Long slopes of creeping waste cover the moun- 
tain flanks far up towards the summits ; craggy peaks of sharp 
form are less common than in the Selkirks or the Alps. 

Climate of Mountains. — On extensive plains the cli- 
mate — especially the temperature and rainfall — changes 
very slowly from place to place, being nearly uniform for 
hundreds of miles together. On the average, one must 
travel from 30 to 60 miles poleward to find a difference 
of 1° in mean annual temperature. The same difference 
is found on niountains by an ascent of only 300 feet. 

Broad plains may have only a scanty rainfall over 
hundreds of miles together. On lofty mountains the rain- 
fall rapidly increases with elevation. Not only because 
they are high, but also because they receive much rain 
and snow, high mountains are usually the sources of large 
rivers. 

Similarity of form and climate over broad plains makes 
the conditions of life nearly uniform over great areas. In 
mountains diversity of form and climate is found within 
small distances, and strong contrasts in the conditions of life 
are crowded close together. 

On account of the lower temperature and the heavier 
rainfall and snowfall of high mountains, their ■ animals and 
plants are unlike those living on the surrounding lowlands. 
On ascending the mountain flanks, hardy cone-bearing trees 
succeed those needing a milder climate. As the limit of 



176 PHYSICAL GEOGRAPHY. 

tree growth or " tree line " is approached, only stunted and 
deformed trees survive. Then comes a belt in which the 
slopes bear grass and Alpine flowers. (Alpine is used to 
refer not only to the European Alps, but also to the animals 
and plants of any lofty mountain.) Following this is the 
snow line, above which some of the snow of one winter lasts 
over the following summer, excluding plant life. The height 
of the snow line is greatest in the torrid zone (18,000 to 
20,000 feet) and decreases towards both poles, reaching sea 
level in the frigid zones. It is remarkable that many plants 
found near the snow line on mountains in the warmer zones 
are also found near sea level in the frigid zone. 

Mountains as Barriers. — High mountains serve as bar- 
riers, separating the climates and the populations of their 
opposite sides. The eastern slope of the equatorial Andes 
has a moist climate because the damp winds from the 
Atlantic, ascending and cooling, give forth a heavy rain- 
fall there ; the western slope has a dry climate because the 
same winds, descending and warming, not only give forth 
no more rain, but eagerly take up whatever moistui-e they 
find on the way. The eastern slope is densely forested ; 
the western slope is for the greater part a desert, except 
in vallej^s watered b}^ streams. 

Moist winds from the Pacific give a plentiful rainfall 
on the westward or windward slopes of the Sierra Nevada 
and the Rocky mountains of the United States. The same 
winds, descending on the eastern or leeward slopes, become 
in winter unseasonably warm and dry (see Appendix H), 
evaporating the light snow of the plains, and laying bare the 
dry bunches of grass, greatly to the advantage of the cattle 
feeding there. The dry wind is called the Chinook. A simi- 
lar wind occurs in the northern valleys of Switzerland, where 
it is called the Foehn. 



MOUNTAINS. 177 

The great populations of India and China, representing 
different races, are s,eparated by the Himalaya and other 
ranges in southern Asia. They are thus so well held apart 
that neither one has had an important influence on the other. 
Lofty mountain ranges thus rank with the oceans in separat- 
ing the inhabitants of the lands. 

When low countries on opposite sides of a high range are 
occupied by different peoples, the mountains commonly serve 
as a natural boundary between the two countries. The range 
as a whole may serve as a rough boundary between uncivi- 
lized nations ; but between civilized nations the crest line 
dividing the rivers of the opposite slopes is often accepted as 
a more precise boundary, as in the Pyrenees between France 
and Spain, where the river divide is generally adopted as the 
national divide. 

When the river divide departs from the main range that 
it was supposed to follow before the mountains were explored, 
the boundary question may give rise to dispute, as recently 
between Argentina and Chile, where a number of Pacific rivers 
rise on the pampas of Patagonia, and cut through the Andes in 
deep gorges. 

The difficulty of crossing lofty ranges gives great im- 
portance to the notches or passes in their central ridges, 
through which travel and traffic may go with less effort 
than over their peaks. The heavy snows of the winter 
may close the passes for several months. In earlier cen- 
turies, when the passes were traversed only by paths, 
houses of refuge were often maintained on the summit by 
monks, as on the famous pass of St. Bernard in the Alps. 

It is chiefly within the last hundred years that well-planned 
roads have been constructed over the chief passes of various 
Alpine ridges. The roads enter the mountains along the 
larger valleys, and then zigzag up the steeper slopes. They 



178 



PHYSICAL GEOGBAPHY 



are carefully laid out so as not to exceed a certain moderate 
grade, about five feet in a hundred. Certain passes are now 
crossed even by railroads, the ascent from the valleys being 
most ingeniously made by curves and ''loops." Sometimes 
the last part of the ascent is avoided by tunnelling the ridge 
under the pass, it being cheaper in the long run to bore 
throusfh than to climb hiarher. 



Avalanches. — The heavy snowfall of winter often over- 
loads the snow banks on the higher slopes, and great 

masses of snow 
slide down to 
lower levels. 
Summer melt- 
ing and rainfall 
also cause slides 
or avalanches 
(aval : to the val- 
ley). Sometimes 
the snow mass 
glides along the 
sloping surface 





Fig. 110. —An Avalanche Path, Selkirk Range, Canada. 



at a moderate speed. Sometimes it leaps from cliffs, and 
falls with a terrible velocity to the valleys below ; a vio- 
lent blast of air bursts outward from beneath, overturning 
trees hundreds of feet beyond the reach of the snow. 

Certain villages in Alpine valleys carefully preserve a 
patch of forest on the slope above them as a protection from 
avalanches. Highways and railways on steep mountain 
slopes must here and there be covered in by long snow 
sheds, over which the snow may slide without blocking or 
injuring the road. 



MOUNTAINS. 



179 



Heavy masses of ice are occasionally detached from gla- 
ciers that end on steep slopes, forming " ice falls." These 
are even more destructive than avalanches of snow. An ice 
fall, over 5,000,000 cubic yards in volume, broke from a 
glacier on the slope of the Altels (Fig. Ill ; see Fig. 109, 
from a photograph taken before the fall) in the Alps in Sep- 




rig. 111. —Path of an Ice Fall in the Alps. 



tember, 1895. It ran down a steep slope two and a half 
miles long, gathered about 1,300,000 cubic yards of rock 
waste on the way, and then rushed across the valley floor, 
dashing far up the opposite slope and falling back again, like 
a wave from a cliff. A bench on the path of the sliding mass 
caused it to leap forward, clear of the ground ; then falling, 
the air beneath was violently driven away, blowing out frag- 
ments of ice and rock and breaking down trees hundreds of 
yards distant. 

Valleys among Mountains. — One of the strongest char- 
acteristics of thoroughly dissected, lofty mountains is the 
activity with which the rock waste is weathered from the 
peaks and cliffs, moved down the steep slopes, swept by 



180 



PHYSICAL GEOGRAPHY. 



the streams along the larger valleys, and washed out upon 
or across the adjoining lowlands. The waste seems every- 
where to be streaming (as the long-lived mountains might 
say) down from the peaks and ridges. The elaborate 
carving of the mountains has been accomplished by the 
long duration of these active processes for ages past. 

The greatest work of erosion is seen in the excava- 
tion of the chief valleys and their innumerable branches. 
Unlike young mountains, where the valleys generally 
follow the troughs between the uplifted blocks or arches, 
lofty mountains are dissected by valleys that often bear 
little relation to the original depressions among the uplifts. 
Just as the peaks and ridges result from the survival of 
the more resistant rocks, so the valleys in thoroughly dis- 
sected mountains generally result from wearing out the 
weaker layers, which have been thoroughly sought for by 
the destructive processes. 



Some of the valleys among high mountain ranges may be 
cut down deep beneath the troughs by which the streams 

were originally lo- 
cated. It is not 
rare in greatly up- 
lifted and deeply 
dissected moun- 
tains to find high 
ridges bearing the 
remnant of a down- 
folded hard layer ; 
the rock arches on 
each side being now 
worn down to deep valleys that have been excavated on 
weak under-lay ers, as in Fig. 112. Thus an original valley 







t- 






Fig. 112. — A Mountain of Down-Folded Layers. 



MOUNTAINS. 181 

floor has come to be a mountain ridge, while the adjoining 
a.rches have been reduced to deep valleys. The importance 
of erosion as a means of producing land forms and the great 
depth to which valleys have been carved are seldom more 
emphatically taught. 

Valley floors among lofty mountains must be at a con- 
siderable height above sea level, especially near their 
heads; for as long as a great volume of waste is swept 
from the upper slopes and washed by torrents down the 
ravines and side valleys, even a good-sized river in a main 
valley cannot cut its channel down to a faint slope, close 
to sea level. The valley line must have a rather rapid 
descent, 50 to 100 feet to a mile, in order to give the 
river a velocity that will enable it to carry away the waste 
that is washed into it. 

In deep and narrow valleys the side slopes are sometimes 
cut so steep that great rock masses may be detached from 
the walls and slip to the bottom, forming landslides. This 
is particularly common where the strata in the valley walls 
slant into the valley. 

In September, 1893, a great landslide occurred in the deep 
valley of one of the upper branches of the G-anges in the 
Himalaya, 150 miles above the city of Hardwar, where the 
river emerges on the plains. In three days 800,000,000 tons 
of rock fell with deafening noise, darkening the air with 
dust, leaving a great bare cavity with steep walls several 
thousand feet high to mark its source, and building a dam 
nearly 1000 feet deep across the narrow valley floor. A lake 
gradually formed on the up-stream side of the dam, and grew 
to be four miles long before it overflowed about a year after 
the slide. 

In the mean time the danger that the lake might burst out 
in a great flood being perceived by the British engineers in 



182 



PHYSICAL GEOGRAPHY. 



charge of the public works of India, the bridges in the lower 
valley were removed ; safety marks were set up on the val- 
ley sides, 100 or 200 feet above the ordinary river level, 
indicating the height above which the flood would probably 
not rise ; and a telegraph line was constructed from the dam 
to Hardwar, to give prompt warning of the outburst. 




Fig. 113. — A Landslide in the Himalaya. 



The flood occurred at midnight, August 26-27, 1894. In 
four hours about 400,000,000 cubic yards of water were dis- 
charged, cutting down the dam nearly 400 feet, flooding the 
valley to a depth of from 100 to 170 feet, and rushing forward 
with a velocity of 20 miles an hour. Many miles of valley 
road were washed away. Every vestige of habitation was 
destroyed in villages along the Ganges above Hardwar. But 
so well was the notice of danger given that only one man lost 



MOUNTAINS. 183 

his life, and that because he would not heed the warning. 
Under a less intelligent control, thousands of people must 
have perished in such a catastrophe. 

Lengthwise and Crossv/ise Valleys. — When a river has 
cut down its valley floor to as moderate a slope as 
the load of waste that it has to carry along will allow, 
it may still wear away its banks, first on one side, then on 
the other. Thus in the course of time the river broadens 
the valley floor. This is es'^ecially true in a valley that is 
worn down along a belt of weak rocks parallel to the gen- 
eral trend of a mountain range ; for these rocks weather 
and wash away at a comparatively rapid rate. 

The crosswise valleys, by which the rivers of the long 
inner valleys find outlets through enclosing ridges, are 
often narrow and steep-walled gorges ; for the ridgemak- 
ing rocks are resistant and weather slowly. The floor 
of a crosswise or transverse valley may be hardly wider 
than its stream; the walls rise steep from the water's 
edge, leaving no room for a road or path on either side. 

It is chiefly in the broader lengthwise valleys that moun- 
tain peoples dwell. When the outlet valleys are narrow 
gorges, the outer world has for centuries been reached only 
by passes over the enclosing ridges ; but modern engineering 
skill has sufficed to build and cut roads and railroads through 
many gorges that were impassable a century ago. 

Earthquakes of Growing Mountain Ranges. — The actual 
process of bending and breaking the rock structures 
within a mountain mass sometimes causes sudden snaps 
and slips of a few inches or a few feet. Tremors of 
greater or less strength then spread in all directions from 



184 PHYSICAL GEOGRAPHY. 

the seat of disturbance, diminishing their intensity as 
they advance. On reaching the earth's surface they are 
felt as earthquakes, producing more or less destruction. 
Shocks of this kind are comparatively common in most of 
the lofty mountains of the world. 

Earthquake tremors travel through the earth's crust with 
great velocity — from 10 to 40 miles a minute ; but as in 
the cases of water waves the actual movement of the earth 
at any point may be only a few inches a second, backward 
and forward. The shocks produced by earthquake waves are 
most violent at places directly over the seat of chief disturb- 
ance. They may be very faint, causing no damage. They 
may be strong enough to be felt violently over hundreds of 
square miles, less distinctly over many thousands, and very 
faintly (by the aid of delicate instruments) all over the earth. 

Earthquakes of moderate violence are still frequent in 
the Alps, occurring 5 to 10 times a year. Five centuries 
ago (1348) a violent earthquake in the eastern Alps caused 
a great landslide by which a valley was barred across and a 
lake formed up stream from the slide. Countless thousands 
of shocks must have been produced during the long ages of 
mountain growth. The association of earthquakes with the 
young tilted-block ridges of Oregon, with the more mature 
mountains of Nevada, and with vigorous ranges like the 
Alps and the Himalaya, is a natural result of the continued 
disturbance or growth of the mountains. 

Inhabitants of Lofty Mountains. — The people vi^ho 
to-day dwell in the valleys of lofty mountains are in 
many cases the descendants of races who formerly occu- 
pied the adjacent lower lands, from which they were 
driven by conquering invaders. Secluded valleys among 
mountains serve as refuges, where pursuit is too difficult 



MOUNTAINS. 185 

to be profitable. There the weaker race long remains un- 
molested, holding little intercourse with the outer world, 
and preserving old forms of speech and old-fashioned 
customs. The invaders occupy the neighboring open 
country; they engage in traffic with the other parts of 
the world and advance in new ways of living. 

The Basques live in the northern valleys of the Pyrenees, 
near the angle of the Bay of Biscay. They are probably 
descendants of the Iberians, an ancient people who occupied 
a large part of Spain and France, from which they were 
driven by invaders even before Csesar made those countries 
subject to Eome, nearly 2000 years ago. The Basque lan- 
guage is the only surviving form of Iberian, and is entirely 
unlike other European languages. 

The Svanetians occupy deep inner valleys in the Cau- 
casus mountains, with dijSiculty accessible from the outer 
country. Their ancestors were an ancient people who occu- 
pied a far more extensive territory, from which they were 
driven back to the mountains many centuries ago. There 
ancient customs and a peculiar language are preserved ; there 
the people still live, entirely apart from the ways of modern 
times. Although daring and patriotic, they are ignorant and 
superstitious. Their wretched houses are dark and dirty ; 
their roads are only rough tracks. Arts and industries are 
of the simplest order ; traffic is only by barter. 

The small country of Switzerland is largely mountain- 
ous. Andorra, a very small independent country in the 
Pyrenees between France and Spain, is a modern instance 
of the many small political divisions that prevailed in 
Europe during the middle ages. These two small moun- 
tainous countries are in striking contrast to the vast extent 
of the Russian dominions, of whose area so large a part 
consists of plains of comparatively even surface. 



186 PHYSICAL GEOGRAPHY. 

The broader valleys within high mountains afford many 
favorable places for settlement and cultivation. The nar- 
rower valley floors are frequently swept over by destruc- 
tive floods ; here the lower slopes of the valley sides are 
commonly selected as sites for villages, and it is often 
necessary to make terraces on the mountain flanks in 
order to gain flat patches of ground for cultivation. 

During winter the valleys among lofty mountains may 
receive a heavy snowfall ; then for a season the people and 
their flocks are gathered in the villages. In summer, when 
the snows are melted from the mountain sides, cattle, sheep, 
and goats are driven up from the valleys to pasture on the grassy 
slopes of the ridges, and hay is carried, often on the backs of 
the mountaineers, down to the villages for winter need. 

In the Alps the condition of the people has greatly 
improved since it came to be the habit of tourists to make 
excursions among the mountains. Excellent roads have been 
built ; good hotels are to be found in little villages ; paths 
lead far up on the mountains, where huts of refuge are con- 
structed to shelter the more adventur- 
ous mountain climbers. Entertainment 
of strangers has come to be an almost 
national industry. 

Many animals survive in mountains 
after retreating from the surrounding 
lower ground. Various species of Ibex 
(mountain-goat) are found on the moun- 
tains of Eurasia, each range having its 
own peculiar species. From a common 

Fig. 114. — Ibes. ^ \ . . 

ancestry on the intermediate lower 
ground the descendants in each range have varied in their 
own way, independently of the others. This is a remarkable 
illustration of the effect of mountains in keeping their inhabi- 
tants apart from the rest of the world ; it may be compared 
with the effect of isolation on islands. 




MOUNTAINS. 



187 



Subdued Mountains. — There are certain mountain ranges 
of moderate heiglit, in which sharp peaks are absent and 
bold cliffs are rare. The slopes are of moderate steep- 
ness, and rock waste covers them almost from base to 
summit. Mountains of this kind do not reach upward 
into a climate very unlike that of their base ; and if not in 
a dry or a frigid region, they may be forest-clad to the top. 

The earthquakes that are common in mountains of active 
growth and the landslides that happen frequently in moun- 
tains where the valley sides are still steep are rare or unknown 




Fig. 115. — The Mountains of North Carolina. 

in these mountains of gentler form. Unlike the vigorous 
forms of lofty mountains in which uplift and erosion are still 
active, the rounded forms of these mountains express subdued 
strength, as if their high peaks and ridges had been greatly 
worn away by the long-continued attack of the weather. They 
may therefore be called subdued mountains. 

The Blue Ridge and other mountains of North Carolina 
are good examples of subdued mountains. No sharp peaks 
tower into the sky. The summits generally rise dome-like 
in rounded outline. Heavy forests clothe their slopes. 



188 PHYSICAL GEOGRAPHY. 

As in all regions of rugged form, out of the way of easy 
travel and active traffic, the people living in the valleys 
among subdued mountains preserve older fashions than those 
of the more open lower country. This is seen in the home- 
spun clothing and in the manner of speech of the IS'orth 
Carolina mountaineers. 

The mountains of Wales make another group of subdued 
forms, but more rugged than the mountains of North Caro- 
lina. Here remain some of the descendants of the Britons 
who were driven from the more open lowlands of eastern and 
central England by Saxon 9,nd Xorman invaders, 1000 or 1500 
years ago. The Welsh language, therefore, represents the 
original language of Britain, while the English language is 
a compound of the speech of the invading peoples. 

The higher parts of subdued mountains remain wooded 
long after the surrounding lowlands are cleared and culti- 
vated. Hence many mountains of this kind in central 
Europe are named for their forests, as the Schwarzwald of 
Germany, literally Black Eorest, but better translated Black 
mountains. Timber from the forests may be sawed by the 
abundant water power in the valleys, and the lumber sent 
out to the more populous lowlands. 

Worn-down Mountains. — In certain parts of the world 
ancient mountain ranges have been almost completely 
worn away. Their disordered rocks, once rising in lofty 
peaks and ridges, and perhaps bearing snow fields and 
glaciers, have been reduced to an almost plain surface, 
little above baselevel and everywhere open to settlement. 

The Piedmont belt of Virginia, between the Blue Ridge and 
the coastal plain, is in many respects an excellent example 
of a worn-down mountain range. It is a plain, not monot- 
onously smooth, but undulating in graceful swells between 
gentle depressions. Bare ledges are seldom seen. The soil 



MOUNTAINS. 



189 



is deep, fine, and fertile, and the district is very generally- 
occupied by farms. The height to which the rock masses 
once rose a.bove the present surface is reasonably estimated 




Tig. 116. — The Piedmont Belt, Virginia. 



as at least one mile ; it may have been two or three. The 
wearing down of these ancient mountains to the rolling plain 




Fig. 117. —Map of the Piedmont Belt, Virginia. 



of to-day has required a period of time compared to which 
that occupied in cutting the Colorado canyon is a brief 
interval. 



190 



PHYSICAL GEOGRAPHY. 



It often happens that the plain surface of a worn-down 
mountain range is here and there surmounted by rounded 
hills or low mountains, 1000 or more feet high, com- 
posed of the most resistant rocks of the whole region. 
These hills are the last remnants of the mountains that 
once towered over the surface of to-day. They may be 
called monadnocks, after a mountain of this kind in 
southwestern New Hampshire. 

Several monadnocks are scattered over the Piedmont plain 
of Virginia, one being shown in Fig. 116. Sometimes the 
remnant mountains have the form of long ridges. The Alle- 
gheny mountains of Pennsylvania are ridges of this kind, 




Fig. 118. — Diagram of the Allegheny Mountains, Pennsylvania. 

formed of the most resistant sandstones of the region, while 
the weaker rocks are worn, down lower, as in Fig. 118. 
These mountains have been uplifted and worn down more 
than once. 



MOUNTAINS. 



191 



It is generally the case that old-mountain lowlands are 
now uplifted above the position in which they stood when 
worn down, so that they form plateau-like uplands. Their 
streams are thus revived into a new period of activity, 
and at once proceed to trench and dissect the upland. Dis- 
sected uplands of this kind, bearing monadnocks in greater 
or less number, are very common geographical forms. 

The Piedmont belt of Virginia now stands several hundred 
feet above baselevel. It is cut across by a number of active 
streams that flow in winding, rocky, steep-sided valleys, from 
100 to 300 feet beneath the upland plain. It is here that the 
tilted rock structures of the ancient mountains are best seen. 

One of the finest examples of an uplifted old-mountain 
lowland is found in the plateau-like Slate mountains of 




Fig. 119. — Gorge of the Rhine in the Slate Mountains, Germany. 

western Germany. The broadly undulating upland is 
generally cleared and cultivated. Here and there the 
more resistant rocks stand up in forest-clad monadnocks 
(M, Fig. 119). The Rhine has cut a deep gorge directly 
through the upland, and the side streams are cutting steep 
ravines in the bordering slopes. 

The valley of the Ehine here consists of an upper trough (T), 
with a narrow gorge (6^) cut in its floor. The ruined castles 



192 PHYSICAL GEOGRAPHY. 

for which the valley is famous stand on the edge of the 
trough, overlooking the inner gorge. The uplift by which the 
cutting of the narrow gorge has been permitted cannot have 
taken place very long ago (as the old mountains would count 
time), for the river has not yet had time to widen its valley 
floor. Ledges that formed rapids in the channel have been 
removed by blasting. 

Soutliern New Hampshire and Vermont, central and 
western Massachusetts, and all of Connecticut include 
many uplands, above wliicli occasional monadnocks rise, 







Fig. 120. — The TTpIand of New England, with Monadnock in the Distance. 

and beneatli which numerous valleys are worn. When an 
observer stands on the uplands, the sky line is seen to be 
comparatively even and independent of the attitude of 
the tilted rocks whose ledges crop out on the valley sides. 
If the valleys were in imagination filled up again to the 
level of the uplands, the worn-down plain of the ancient 
mountains of New England would be restored. 

The plain does not now stand close to the baselevel with 
respect to which it was worn down. It has been uplifted into 
a slanting position, so that it slowly rises from sea level at 
Long Island sound to a height of from 1400 to 1600 feet on 



MOUNTAINS. 



193 



the northern boundary of central and western Massachusetts. 
The valleys have been carved in consequence of this uplift. 
They are shallow near the coast, but deep (800 to 1000 feet) 
in the interior, where the upland is higher. They are narrow 
where the rocks are resistant, but wide open where the rocks are 
weaker. The chief of the wider valleys is that of the Connecti- 
cut river, excavated along a belt of relatively weak sandstones. 
The monadnocks that crown the uplands are forested and 



f-^^^^t^ ^^^^.f^^pfi^ ,^1-^,0^^ ^^ 




Fig. 121. — Valley of the Deerfield in the New England Upland. 



uninhabited. The uplands have a scattered farming popula- 
tion, here and there gathered in small villages. The valley 
sides are generally wooded, but sometimes hold sloping fields. 
The larger valleys contain many villages and cities, and lead 
the chief roads and railroads. Here is gathered the more 
active manufacturing and commercial population of New 
England. The valley sides are often quarried for resistant 
building stones, like granite ; the broad Connecticut valley 
floor yields brown sandstones, easily cut and carved, and much 
used for ornamental architecture. 



194 PHYSICAL GEOGRAPHY. 

The Highlands of Scotland are a bolder example of an 
old, worn-down mountain region, now uplifted again and 
dissected by numerous deep valleys. Their sky line is 
rather uneven, and it is not probable that the old moun- 
tains were ever worn down very low ; yet the sky line is 
smooth compared to the excessive breaking, tilting, and 
folding that the ancient rocks of the Highlands have 
suffered. The valleys are from 2000 to 3000 feet deep. 
The smaller branch valleys are called glens. The moun- 
tains of to-day are the result of cutting down the valleys 
and glens between them, just as in the so-called " moun- 
tains" of the dissected Allegheny plateau of West Virginia. 

The form of the Highlands has for centuries had a strong 
influence on the history of the Highlanders. Like so many 
other moimtaineers, they are the descendants of an early 
people driven from the Lowlands by invaders. Taking refuge 
in the Highlands, they have not lived on the mountains, but 
in the deep glens. Being thus divided into small communities 
or clans, the members of each clan became closely associated 
and devoted to their local leaders ; and this way of living has 
given the word " clannish " to our language. It was difficult 
to survive in their rugged country ; hence the survivors 
became hardy and thrifty. The Lowlands on the south are 
occupied by descendants of the invaders ; their people and 
language are of different stocks from those of the Highlands. 
Thus arose the long feuds between the Highlanders and 
Lowlanders, narrated in Scott's novels and poems. Now 
that warlike strife has ceased between them, and means of 
travel have increased, many of the Highlanders have left 
their rugged glens and emigrated to other parts of the world. 

The ancient rocks of worn-down mountains often con- 
tain deposits of rare minerals and valuable ores. These 



MOUNTAINS. 195 

have been formed by slow chemical changes that went on 
deep within the crust of the earth when the rocks now 
visible were buried far beneath the surface. As a conse- 
quence, mining often flourishes in regions of this kind. 

The Erzgebirge, or Ore mountains, of Germany are a worn- 
down and again uplifted ancient mountain range. Many 
valuable minerals occur in their rocks, and mining has been 
carried on there for a long time. Indeed, this art is so gener- 
ally practised in the subdued or worn-down and uplifted 
ancient mountains of Germany that the German word for 
mining is Bergwerk, or mountain-work. 

The gold-bearing veins in the Sierra Nevada of California 
and in the Klondike district of Alaska both occur in ancient, 
worn-down mountains, now uplifted and again more or less 
dissected. The important deposits of iron ore in northern 
Michigan and Minnesota are similarly situated. 

Embayed Mountains. — A mountain range near a con- 
tinental border will be partly covered by the sea if a 



Fig. 122. — Model of Embayed Mountains. 



movement of depression lowers the level of the land. 
The effect thus produced will be similar to tliat observed 



196 PHYSICAL GEOGRAPHY. 

in the half-drowned coastal plain already described. The 
valley floors and mountain flanks will be submerged to a 
greater or less depth, and many long bays will enter 
between outstretching promontories and islands. The 
wasting of the ridges still standing above sea level will 
continue as before ; deltas will be formed at the bay heads, 
and sea cliffs will be cut on the headlands, with reference 
to the new baselevel. 

A partly drowned mountainous district has a coast line 
of great irregularity. The long bays, called fiords., pro- 
vide many protected harbors, but their waters are often 
inconveniently deep for anchorage, and the lands may be 
too steep for easy settlement. The outlying islands tempt 
exploration from the mainland. It may well be believed 
that the art of navigation of the open sea was developed 
by a people inhabiting an irregular coast. 

The coast of British Columbia and southern Alaska is bor- 
dered by high mountains, into whose valleys the sea now 
enters in long fiords. Lateral ridges, separated from the 
mainland by water channels or sounds, stand forth as islands. 
A navigable " inner passage " is thus provided for steam 
vessels, well protected from the rough water of the open 
ocean. The steep mountain sides, descending rapidly beneath 
the sea, generally offer no flat ground for settlement ; but 
most of the fiords now contain delta plains where streams 
enter their heads ; here villages find convenient sites. 

Since the Highlands of Scotland were uplifted and dis- 
sected, a moderate depression has submerged the lower valleys 
and carried the sea against the mountain flanks, where strong 
cliffs are already cut on the headlands by the stormy waters 
of the Atlantic. The fiords occupying the submerged valleys 
are here known as sea lochs (loch = lake). Although adding 
greatly to the beauty of the scenery, the change has decreased 



MOUNTAINS. 197 

the habitability of the coast region, for many valley floors 
that might have been occupied by fields and villages are now 
drowned. The deltas growing at the head of the sea lochs 
form convenient plains for cultivation, but they are seldom 
of great extent. 

Example for Review. — The highlands of northern Wis- 
consin are part of a very ancient mountain region that 
was worn down to a lowland of moderate relief before 



Fig. 123. — Diagram of Baraboo Ridge, Wisconsin. 

the rock layers of the ancient coastal plain of southern 
Wisconsin were formed. Their formation as marine sedi- 
ments was permitted when the southern part of the old- 
mountain region was depressed and drowned beneath an 
ancient sea, the drowned old-mountain lowland serving 
as the foundation on which the covering strata were laid 
down. At that time a monadnock that rose above the 
old-mountain lowland remained for a time as an outlying 
island; but as the depression of the region continued, it 
was drowned and finally buried beneath the sea-bottom 
deposits. 



198 PHYSICAL GEOGRAPHY. 

To-day tlie upper strata of tlie ancient coastal plain 
have been greatly worn away in the central and southern 
part of the state, and the long-buried monadnock is now 
revealed again as an isolated mountain, known as Baraboo 
ridge, rising boldly above the floor of the inner lowland. 

The lowlands and uplands of the ancient coastal plain 
are for the most part fertile farming districts ; the unburied 
monadnock stands apart as a forested ridge, quarried for 
its hard stone. It rises through the weak strata of the 
inner lowland like a long-preserved monument of the earth's 
early history. 



-f- 



CHAPTER VIII. 

VOLCANOES. 

The Violent Peocesses oe Natuee. 

Most of the processes of nature go on without vio- 
lence. The usual movements of the winds and currents, 
the flow and ebb of the tides, the rise and fall of the 
lands, the weathering and washing of rock waste are all 
so placid that we gain confidence in the earth as a safe 
home to live in. But sometimes natural processes of a 
more violent behavior are witnessed. Hurricanes and 
tornadoes bring destructive winds and torrential rains, 
flashes of lightning and peals of thunder. Landslides 
rush down mountain sides, overwhelming the valleys 
below. Now and then the rocky crust beneath us quivers 
and trembles in earthquakes. Great waves occasionally 
roll in from the sea and sweep over low coastal lands. 
Here and there volcanoes burst forth with terrible com- 
motion. Nature then seems frightful and desti'uctive. 
Those who are overtaken by such disasters struggle 
against them, hopefully awaiting the return of the more 
peaceful conditions under which their habits of life have 
been -formed, for man could not survive it if he were 
always battling against the wilder forces of nature. 

Of all natural catastrophes the explosive eruption of a 
great volcano is the most terrible. The air resounds with 
its roaring. The sky is darkened and the sun is hidden 



200 



PHYSICAL GEOGRAPHY. 



by clouds of dust blown from the crater. The sea is 
burdened with floating ashes. Glowing streams of lava 
■flow down the flanks of the volcano, driving away every- 
thing that can take flight before them. Even the earth 




Fig. 124. —Vesuvius in Eruption. 



around is made to tremble as the gases and the lavas burst 
out from their deep sources. No wonder that ignorant 
races of men have imagined struggling giants to be impris- 
oned under active volcanoes, nor that even the most 
learned are baffled when trying to account for these terrific 
displays of natural forces. 



VOLCANOES. 201 

But violent as a volcanic eruption may be, it weakens, 
and in time ceases. The sky clears, the sun shines again, 
and Nature once more goes on in her quiet tasks. As the 
years pass by and a soil is formed on the weathered ashes 
and lavas, plants clothe their surface and man comes to 
dwell on the flanks of the volcanic mountain. The strug- 
gling giant within is forgotten ; fields and villages occupy 
the slopes that once trembled and glowed in eruption. 

In the long history of the human race many disasters 
from volcanoes and earthquakes have been encountered, 
and the race has gradually gained in courage and intelli- 
gence as these and other trials have been survived. Les- 
sons of this kind are hard to learn, but they seem to be 
among those that the earth has in store for us. 

The Growth and Dissection of Volcanoes. 

Young Volcanoes. — Volcanoes are formed by the ascent 
of molten rock, called lava, through fractures or passages 
leading from unknown depths through the earth's crust to 
its surface, on the land or on the sea floor. The eruption 
of the lava is generally accompanied by explosions of 
steam and other gases. 

The cause of volcanic eruptions still needs as much study as 
that of the various displacements of the earth's crust referred 
to on earlier pages. It is believed by many that the ascent 
of molten lava from its deep source is chiefly caused by pres- 
sures similar to those which cause movements in the earth's 
crust. As the lava nears the surface and meets water in greater 
or less quantities, explosions of steam take a violent part in 
the eruptions. 



202 



PHYSICAL GEOGBAPHY. 



The early growtli of a volcano has occasionally been 
observed. The outburst is preceded and accompanied by 
earthquakes, which indicate the breaking of an upward 
passage through the underground rocks, before hot lavas 
make their appearance at the surface. When the eruption 
is accompanied by gaseous explosions, much of the lava is 
blown into fragments, of which the smaller are called ashes 
or cinders. The larger blocks and the coarser ashes 
accumulate in a conical heap, or volcano, frequently having 
remarkable regularity of form, a cup-shaped hollow or 
crater being kept open over the vent by the oiitbursting 
gases. The finer ashes or dust may fall far a,way. When 
the eruption is less violent, the lava runs forth more 
quietly in a stream or flow following the slopes of the 
ground. Explosive and quiet eruptions may alternate 
in irregular succession. 



Monte NuGvo (New Mountain) is a small volcano that was 
formed on the north side of the Gulf of Naples in Italy in 
1538. Earthquakes occurred thereabouts for two years before 

the eruption, when in 
a week's time a cone 
was built up 440 feet 
high, half a mile in 
diameter at the base, 
and with a crater over 
400 feet deep. Masses 
of lava "as large as 
an ox " were shot into 
the air by the bursting of great bubbles of gas or steam that 
ascended through the lava in the vent. Finer ashes fell over 
the country for several miles around. The people of the 
neighboring villages fled in terror from their homes. 




Fig. 125. — Monte Nuovo. 



VOLCANOES. 203 

A greater eruption took.place in Mexico in 1759, when the 
volcano Jorullo (pronounced Ho-rul-yo) was built on the cen- 
tral plateau, burying fertile fields of sugar cane and indigo. 
The outburst was preceded by earthquakes ; the eruption 
continued half a year, building six cones and pouring out 
extensive lava flows. The highest cone, Jorullo, rose 700 
feet above the plateau. The flows retained a perceptible 
heat for over 20 years. 

Many examples might be given of marine eruptions. In 
1867 a shoal was discovered among the Tonga Islands of the 
Pacific (latitude 20° 20' S., longitude 175° 20' W.), the surround- 
ing sea floor being about 1000 fathoms deep. In 1877 smoke 
was seen ascending from the sea surface over the shoal. In 
October, 1885, an island had been formed two miles long and 
200 feet high. At this time a terrific eruption was in prog- 
ress, enormous clouds of constantly changing form rising over 
the island. The shocks of the explosions were felt on neigh- 
boring islands, and the sound was heard 200 miles away. As 
the island consisted chiefly of ashes, it has since then been 
rapidly consumed by the waves and will soon disappear, 
unless new eruptions occur. 

Most volcanoes have not been observed in their early 
growth, yet even if not now in eruption, so perfectly do 
they correspond in form and structure with such examples 
as Monte Nuovo and Jorullo that no doubt can remain as 
to their origin. 

In northern California there is a cinder cone of remark- 
ably perfect form and certainly of recent date, although there 
is no record of its eruption. The cone, built of loose ashes, 
is 2000 feet in diameter at its base, and rises 640 feet to a 
circular rim enclosing a crater 240 feet deep. It is perfectly 
barren. Although of moderate height, its ascent is difiicult, 
as the ashes slide under a man's weight. A stream of lava 
emerges near the base of the cone, and, flowing westward into a 



204 



PHYSICAL GEOGRAPHY. 



neighboring valley, forms a lava field a mile wide and nearly 
three miles long. The surface of the field is so covered with 
great clinkery blocks of lava as to be almost impassable. It 
is still unweathered and barren. The edge of the field is a 
steep clinkery slope 100 feet high. It obstructs a stream 
from the south, which forms Snag Lake, so called from the 
dead trees still standing in it. The lake outlet runs north 
along the west edge of the lava. On all sides the surface of 
the country is covered with a layer of volcanic ashes and 




Fig. 126. — Cinder Cone ajid Lava Flow, California. 



dust, six or more feet deep near the cone, thinner and finer 
further away, yet recognizable at a distance of eight miles. 
From the size of trees growing on the ashes, it is estimated 
that the cinder cone was built about 200 years ago. The 
lava flow is younger, but none of the Indians or early 
settlers thereabouts (1845) observed its eruption. 

Volcanoes are unlike the structures thus far described, in 
being composed of materials that have been forced up, 
melted, through vents (pipes or fissures) in the rocky crust 
of the earth and built upon a land surface or a sea floor. 
They are peculiar in their relatively rapid formation, so 
that much attention is attracted to their manner of growth. 
Mountains of tilted or folded structure that still possess 
their original form, little changed by denudation, are great 



VOLCANOES. 205 

rarities. But many volcanoes have been built so rapidly 
and so lately that their surface is very little affected by 
weathering. 

Great Volcanoes Many large volcanoes, whose first 

eruption must have occurred many thousands of years 
ago, are still active. After periods of more or less com- 
plete rest, they burst forth again, blowing out showers of 
ashes, building their cones to a height of 10,000 feet or 
more, and adding new lava streams to their flanks, so as 
to gain a diameter of 10 or 20 miles or more at the base. 
The melted lava often breaks forth from the mountain 
side and flows down to gentler slopes on the flanks and 
out upon the surrounding country; thus the cone as a 
whole comes to have concave slopes and a rudely bedded 
structure of ashy and dense lavas. All the greater vol- 
canoes of the world are the product of many eruptions. It 
is probable that the periods of rest have been much longer 
than the spasms of activity. 

A rough classification of volcanoes groups them as active, 
when they are frequently in eruption ; dormant (sleeping), 
when now at rest, though giving signs in hot springs and sul- 
phurous vapors that activity may be resumed ; and extinct, 
when they give no indication of recent or future activity. It 
is not possible to make certain distinction between the last 
two classes ; great eruptions have taken place in volcanoes 
after all signs of activity had ceased. 

The steam issuing from a volcano is condensed in heavy 
clouds. At night the glowing lava, white-hot in the 
crater, yellow or red on the flanks of the cone, illuminates 
the clouds, often giving the appearance of flames. Showers 



206 



PHYSICAL GEOGRAPHY. 



of ashes may bury villages, fields, and forests, as they 
chance to fall. The commotion in the atmosphere during 
a violent eruption often causes rainfall. The floods thus 
supplied may be increased by the water from melted snow 
on the upper slopes of the cone, and occasionally by hot 




Fig. 127. — Excavations in Herculaneum. 

water thrown out from the crater itself. The floods 
gather the fresh-fallen dust and ashes, producing muddy 
torrents that overwhelm the lower lands. 

At the eruption of Conseguina, Central America, in 1835, 
ashes destroyed trees and dwellings 25 miles south of the 
volcano ; thousands of cattle and innumerable wild animals 
and birds were killedi Lava blocks in fragments 5 or more 



VOLCANOES. 207 

feet in diameter are strewn for 10 or 15 miles around the 
great cone of Cotopaxi, Ecuador. 

A tremendous eruption of Galung-gung, a forested volcano 
in a populous part of Java, took place in 1822 ; torrents of 
hot water, mud, and ashes rushed down the valleys, flooding 
the rivers and drowning a great number of men and animals ; 
for 24 miles not a trace of numerous villages and plantations 
was left. 

The first recorded eruption of Vesuvius, a.d. 79, darkened 
the sky with its ashes. The ancient city of Pompeii was 
buried in ashes and about 2000 persons (estimated at one- 
fifteenth of the population) were killed. Herculaneum, near 
by, was overwhelmed with torrents of ashy mud. After 
being long forgotten and overgrown by modern villages, 
parts of these cities have been laid bare by excavations in 
this century, affording many illustrations of ancient architec- 
ture and of ancient modes of living. 

E|rthquakes in Volcanic Districts. — The shocks of a 
violent eruption may shatter the volcano, breaking its sides 
and causing great landslips. The earthquakes thus caused 
are felt for many miles around the volcano. The explod- 
ing gases produce thundering sounds, sometimes audible 
for hundreds of miles. 

Besides the earthquakes directly produced by the explosive 
eruptions of volcanoes, it is probable that many other earth- 
quakes in volcanic districts are the result of disturbances 
within the crust of the earth not directly connected with 
volcanic action. The numerous earthquakes of Japan and 
Italy sometimes accompany eruptions, but are more frequently 
independent of all visible eruptive action. 

Great destruction is caused by earthquakes in regions that 
are frequently shaken. In southern Italy 20,000 lives were 
lost in the earthquake of 1688 ; 49 cities and villages were 



208 PHYSICAL GEOaRAPHT. 

destroyed, and 93,000 persons were killed in the earthquake 
of 1693 ; 32,000 persons were killed in a district having a 
population of 166,000 by the earthquake of 1783. 

Distribution of Volcanoes. — Volcanoes generally occur 
near the sea coast or on the sea floor, but a considerable 
number of cones and flows are known far in continental 
interiors. Volcanoes are more numerous on the borders 
of the Pacific Ocean and of the mediterranean seas than 
on the coasts of the Atlantic, but many volcanic islands 
are known in the Atlantic as well as in the Pacific and 
Indian oceans. 

It is estimated that over 300 volcanoes are now active, 
about 100 of these standing on the continents. Nearly all 
the high oceanic islands, far from the continents, are of vol- 
canic origin. Soundings have discovered a number of conical 
mountains rising from the sea floor, but not reaching the sur- 
face ; their form leaves little doubt that they are volcanoes. 
Dacia Bank, east of Madeira, rises with steep slope from the 
Atlantic floor, over 1000 fathoms deep, to within 50 fathoms 
of the surface. 

In continental interiors extinct volcanoes, young cinder 
cones, and barren lavas are known on the plateaus of Arizona, 
300 miles from the ocean ; in Colorado, 800 or more miles 
inland ; in Tibet, 500 or more miles inland. Several active 
volcanoes in Mexico, Central America, and elsewhere are so 
far from the coast that direct connection with sea water should 
not be regarded (as it has been) necessary to eruptions. 

Like other lofty mountains, volcanoes rise high enough to 
possess different climates at successive heights. Mt. San 
.Francisco, a volcano built on the plateau (5000 to 6000 feet 
elevation) south of the Colorado canyon, rises 6000 feet 
above the desert uplands and bears dense forests on its 
slopes. ' Its summit ascends above the tree line, bearing 



I 



VOLCANOES. 



209 



patches of snow most of the summer. Among the Alpine 
plants there collected, nine are of the same species as those 
living near sea level in Greenland. Lofty volcanoes near the 
equator in South America and Africa bear snow on their 
summits. 

Islands formed by the growth of volcanoes in mid-ocean 
are often bordered by wave-cut cliffs, so that it is almost 
impossible to find a landing place on their shores. Being 
nearly inaccessible, as well as 
distant from the continents, they 
are all the more lonesome. St. 
Helena, a volcanic island in the 
south torrid Atlantic, was for this 
reason a well-chosen place for the 
imprisonment of the emperor 
Napoleon. 

A remarkable instance of the 
effect of isolation on the occu- 
pants of a remote volcanic island 
is seen in the language of the 
people of Iceland. Icelandic, 
Norwegian, Swedish, and Danish 
were all one language a thousand 
years ago ; but while the isolated Icelandic has preserved 
its ancient form with slight change, the languages of the 
continental countries have been much modified ; that of Den- 
mark especially having been affected by the neighborhood of 
Germany. 




Fig. 128. 



A Volcanic Island (section 
and plan). 



Lava Flows. — Great flows of lava sometimes run 
beyond the base of the volcano in which they break 
forth. Their surface is comparatively smooth, if it remains 
unbroken after first cooling, but extremely ragged and 
clinkery, if the first crust is repeatedly broken by con- 
tinued movement. The edge of a clinkery flow may form 



210 PHYSICAL GEOGBAPHT. 

a bluff 100 feet or more in height. On the Uinkaret 
plateau of the Colorado canyon districts stands a throng 
of volcanic cones, from which broad streams of lava 
descend the bordering cliffs in black cascades and form 
barren lava floods on the lower Sheavwits plateau on 
the west. The eruptions are therefore younger than the 
breaking of the plateaus. 

In 1783 a great flood of ^lava rose from a deep fissure in 
Iceland, the lava issuing tranquilly for the most part, flow- 




Fig. 129. — Lava Flows on the Plateaus of Arizona. 

ing away in vast sheets on each side, and advancing in 
streams far along the lower valleys. Hundreds of small 
cones were built over the fissure, which was 20 miles long. 
In the course of ages successive lava floods of this kind have 
built up the plateau of Iceland of generally level aspect, the 
loose slaggy cones of earlier eruptions being gradually buried 
under later sheets. 

Two lava streams of the eruption of 1783 in Iceland flowed 
down valleys 45 and 60 miles from their source, gaining a 
depth of several hundred feet where the valleys were nar- 
row, and spreading out in lake-like plains where the valleys 
were open. The water of side streams was dammed and 



VOLCANOES. 



211 



rose in lakes. Twenty villages were destroyed by the floods 
of lava or water ; 9000 persons (about one-seventh of the 
island's population) and a great number of cattle perished, 
not only at the time of the eruption, but afterwards during 
a famine caused by the burial of the pastures and by the 
desertion of the coast by fish. 

The form assumed by successive lava flows in building a 
plateau is sometimes imitated on a cold winter night when 
trickling streams of water, supplied by daytime thawing, are 
frozen as they advance. If the water is artificially colored 
successive flows are made plainly visible. 

Lava floods, thousands of square miles in area, have 
been poured forth in Idaho, Oregon, and Washington, 
where they form an extensive plateau in a broad depres- 
sion among the surrounding mountains. As they cannot 
be traced to any source in volcanic cones, they are thought 
to have come from fissures now concealed and long unused. 

Between the Columbia and Snake rivers, in eastern Wash- 
ington, the plain surface of the lava flood meets the enclosing 
mountain s'^ just as the sea 



meets ahalf-drowned moun- 
tain range. The lava forms 
level bays between the 
ridges ; the ridges stand 
forth like promontories ; 
outstanding peaks rise like 
islands over the plain. A 
rugged mountainous basin 
has thus been converted 
into a plateau. Part of 
the lava plain has been up- 
lifted in dome-like form to 
a greater height than the 
rest, and is now deeply dissected by valleys 
called the Blue mountains (B, Fig, 130). 




Pig. 130. — The Lava Plateau of Idaho, Oregon, 
and WaBhington. 



This part is 



212 



PHYSICAL GEOGRAPHY. 



Calderas. — In some volcanic regions the high central 
part of a cone is replaced by a broad and deep basin, or 
caldera, from 1 to 5 or more miles in diameter, only the 
lower rim of the cone remaining. The inner walls of the 
rim exhibit the broken edges of lava beds, which slope 
outwards from the lost cone on whose flanks they were 
formed. 




Fig. 131. — Diagram of a Caldera. 



When extensive deposits of lava blocks and ashes lie in 
the surrounding country, it is thought that the cone was 
destroyed and the caldera was formed chiefly by violent 
explosive eruptions. When such deposits are absent, it is 
thought that the caldera was formed by the caving in of the 
central area, on account of the withdrawal of a large body of 
lava from beneath. 

The Azores, a group of volcanic islands in the North 
Atlantic, contain a number of large calderas, whose floors 
are partly occupied by villages and fertile fields and partly 



VOLCANOES. 



213 




by lakes. Other examples are known in Italy, the Hawaiian 
islands, and elsewhere. 

Deception island, in the .--''"' ""■. 

South Shetland group, beyond 
Cape Horn, is the high rim of 
a caldera, breached on one side 
by a narrow gap, which gives 
entrance to a quiet circular 
bay. Layers of ice are to be 
seen between beds of ashes 
and lava on the caldera walls. 

The cone of Vesuvius has 
been built in a large caldera of 
more ancient origin. The cone 
buries one side of the caldera 

rim, the other side being known Fig. 132. - DeceptioB island, a voicamc 
as Monte Somma. '^^"^''^ 'pi^" ^""^ section). 

Dissected Volcanoes. — Active streams running down 
the slope of volcanic cones carve ravines on their flanks. 
Many ravines are formed during the periods of rest in the 
growth of the great volcanoes, only to be filled again by 

later eruptions of 
lavas and ashes. 
After eruptions 
cease, the ravines 
deepen more and 
more, leaving sharp 
ridges between 
them, and at last 
dissecting the cone so deeply as to leave little appearance 
of its original shape. Hence, as in other geographical 
forms, it is important to describe volcanoes with due 
regard to their stage of growth or of decay. 




Fig. 133. — The Cone of Vesuvius in the Caldera 
of Monte Somma. 



214 



PHYSICAL GEOGEAPHY. 



Mt. Shasta, in northern California, is furrowed on all sides 
by gigantic ravines, but its conical form is still well preserved 
(Figs. 134, 135). Many meadows about its base mark the 
site of lakes formed by lava-flow barriers, and now filled and 
drained. The best agricultural land of the region is of this 
origin. 




Fig. 134. — Contour Map of Mount Shasta, CaUfomia. 



Mt. Hood, Oregon, is so deeply dissected by radiating 
valleys between sharp radial spurs that its form has become 
very irregular, A number of extinct and more or less dilapi- 
dated volcanic cones surmount the plateaus of Arizona and 
New Mexico, Mts. San Francisco and Taylor being among 



VOLCANOES. 



215 



the best examples. The Cantal, an ancient Tolcanic cone 
about 40 miles in diameter on the central plateau of France, 




Fig. 135. — Mount Shasta. 



is cut to pieces by radiating 
valleys. Its present height is 
but a small part of the original 
height, judging by the atti- 
tude of the slanting lava beds 
in the radial ridges. A rail- 
road and a highway, entering 
by a valley from the southwest, 
run almost through the center 
of the dissected cone on a low 
pass, and depart by a valley 
to the northeast. 

One of the most superb 
calderas in the world is 
that which contains "Crater 
lake" in southern Oregon. 




Fig. 136. — Mount Hood. 



216 



PHYSICAL GEOGRAPHY. 



Its sides were deeply scored by radial ravines before the 
summit of the cone was destroyed in the production of 
the caldera (probably by falling in), for the ravines as well 
as the lava beds are distinctly cut off by the high cliffs of 
the caldera wall. A little cone, built by a small eruption 
after the caldera was made, forms Wizard island in the lake . 




Fig. 137. — Contour Map of Crater Lake, Oregon. 

Volcanic Necks and Dikes. — Even when the volcanic 
cone is entirely worn away, the neck or column of lava that 
rose through a tube-like passage from deep within the earth 
may still be seen. The lava neck is often harder than the 
enclosing rock, and it then retains a considerable height 
above the surrounding worn-down surface, standing up as 
a butte. In the same way, the lava that rose in a fissure 
may in time come to stand up above the adjacent surface 
like a natural wall, structures of this kind being called dikes. 



VOLCANOES. 



217 



The broad valley plain of the St. Lawrence in southern 
Quebec is surmounted by a number of strong volcanic buttes 
rising several hundred feet over the lowland, and visible 



M&t^^^^ 




Tig. 138. — Monnt Johnson, near Montreal, Canada. 

for many miles across its flat surface. One of them gives 
its name to the city of Montreal (Mount Eoyal). All of 
them testify to the great denudation of the surrounding 




Fig. 139. — Volcajiic Necks, Arizona. 



region, for although the lavas rise high above the plain, they 
give no evidence of surface overflows, such as must have 
occurred if the region had had its present form at the time of 
eruption. 



218 



PHYSICAL GEOGRAPHY. 



Volcanic necks are common on the plateaus of !N"ew Mexico 
and Arizona, where they attain a height of from 1000 to 2000 
feet above the surrounding surface, with diameters of a quarter 
or a half mile. 

Dissected Lava Plateaus. — The great lava plateau of 
Idaho, Oregon, and Washington is trenched by many 
rivers whose courses are extended across the upland from 
their source in the adjoining mountains. The canyon 
of Snake river, along the boundary between Idaho and 




Fig. 140. — Dissected Lava Plateau of Southern India. 



Washington, 4000 feet deep and 15 miles broad, rivals 
the Colorado canyon, except in varied coloring. Buried 
mountain peaks are revealed in the canyon walls ; one of 
them rises 2500 feet above the river and is covered by 
1500 feet of bedded lava. 

Between some of the lava beds are laj^ers of sand and 
gravel or of volcanic dust and ashes. Petrified tree stumps 
and trunks occur in some of these layers, showing that there 
was time enough in the intervals between successive lava 
floods for the formation of soil and the growth of forests. 



VOLCANOES. 219 

The young mountains of southern Oregon are broken and 
tilted blocks of this great lava plain. 

An extensive lava plateau occupies southwest India ; its 
western margin is deeply dissected by streams fed by the 
heavy rains of the summer monsoon. Here, as in Oregon, 
the horizontal layers of dense lava form cliffs, while the 
more ashy layers are weathered back into slopes and plat- 
forms, thus imitating the forms of the dissected plateaus of 
Arizona. 

The Faroe islands (Danish, meaning sheep) are the half- 
drowned remnants of a deeply dissected lava plateau origi- 
nally resembling the lava plateau of Iceland, whose nearly 
level lava beds form the tables of the several islands. The 
exposed outer coasts are cut back into great cliffs from 
1500 to 2000 feet high. The harborless outer islands are 
reached with difficulty, their small population being often 
storm-bound for weeks together. The eggs of sea birds 
nesting on the cliffs constitute an important article of food 
supply, and the bird rocks are valuable property for the vil- 
lages to which they belong. The hardy custom of descending 
to the nests by a rope let down from the cliff top is here 
practised. 

The Giant's Causeway in northern Ireland is on the margin 
of a dissected lava plateau, whose cliffs descend boldly to the 
sea. The name is given because the lava beds are cracked or 
"jointed" so that their surface imitates an artificial pavement 
or " causeway." 

Lava Table-Mountains. — Lava flows occupying valleys 
near the base of volcanoes frequently weather and waste 
more slowly than the adjoining rocks. Hence as the 
region is worn down it may happen that the flows come 
to a stand above the adjacent country in the form of table- 
mountains, or mesas, flat topped and rimmed around with 
a cliff and talus slope. The volcano from which the flow 



220 



PHYSICAL aEOGEAPBY. 



issued may have been completely worn away, the table- 
mountain standing quite apart from the neck or dike that 
marks its source, as in Fig. 141. 

Many lava flows of the extinct volcanic district in central 
France are thus converted into flat-topped ridges and iso- 
lated mesas. On one of the mesas the ancient Gauls built 




Fig. 141. — Diagram of a Young Volcano in the Background, changed by EroBion to 
Lava-Capped Mesas in the Foreground. 



the town of Gergovia, where they long resisted the attack of 
the Romans under Caesar, the cliff rim of the mesa serving 
as a natural fortification. 

A number of table-mountains capped with long lava flows 
occur on the western slope of the Sierra Nevada of California. 
The gravels that lie in the ancient valley troughs beneath 
the lava flows have been mined for the grains of gold that 
they contain. Human relics, chiefly in the form of stone 
mortars, have been found in these gravels, showing that man 
occupied the region long ago, before the time of the lava 
eruptions. 



Example for Review. — The gently rolling plains of 
eastern Montana are trenched by the narrow and steep- 
sided valleys of the Missouri river and its branches. The 



VOLCANOES. 221 

upland surface is so even over large areas and so little 
broken by valleys, except near the larger rivers, that it 
might at first sight be taken for a young plain raised from 
the sea in a recent stage of the earth's history. But here 
and there buttes, dikes, and mesas of lava surmount the 
plain, telling clearly that the surface of the region was 
once much higher than now, for the dikes and buttes mark 
fissures and tube-like passages that were once enclosed 
by extensive rock layers, now removed, and the mesas 
are the remnants of lava flows that ran down from some 




Fig. 142. — Diagram of Dike and Mesa. 

volcanic source to the lowest ground they could reach. 
Hence the gently rolling plain must be an old, worn-down 
surface, and when worn down it must have stood at a 
moderate altitude above the sea. The narrow valleys 
now cut beneath the denuded surface show that the 
whole region has been broadly uplifted after it was worn 
down. 

The thin grass of the treeless plains gives pasture to 
herds of cattle that range from stream to stream. The 
dikes and mesas are rocky and barren. The valley floors 
contain fertile fields of small breadth, and here the houses 
and villages of the region are generally located. 



^ 



CHAPTER IX. 

RIVERS AND VALLEYS. 

The Lifelike Behavior of Rivers. 

It is natural that to one who is ignorant of the carving 
of land forms from their youth through maturity to old 
age the surface of the earth should seem lifeless, for it is 
carved so slowly that even an old man can see no change 
in the form of the hills and the valleys around the home 
of his boyhood. But every one may recognize the lifelike 
behavior of rivers. In possessing active movement they 
imitate one of the most interesting " characteristics of ani- 
mal life, and thus they seem to have a life of their own. 
Ascend a river and trace its branches to their many sources, 
even to the smallest brooks and rills ; they are all found 
to be busy bearing tribute to the main stream. Follow 
the river down its valley, and its growing volume, flowing 
steadily onward, leads as if with conscious purpose to the 
sea. The change of behavior from the active upper waters 
to the sedate lower current suggests that we might 
describe our own growth from youth to old age in terms 
that apply to the " river of life." Indeed the part that 
rivers take in the work of the world is so full of activity 
that they enter the figures of poetic literature even more 
than great mountains or vast oceans. 

The more rivers are studied, the more wonderful their 
place in the system of nature is found to be. They wash 



BIVER8 AND VALLEYS. 



223 



along in every part of their course some share of the waste 
of the land on the way to the sea. They work untiringly. 
Mountains may tower aloft where the crust of the earth 
has been upheaved by irresistible forces from within ; but 
the weather attacks them, the clouds gather around their 
summits, rain and snow fall upon them, and the streams 
and rivers bear off their waste until they are worn away. 




Fig. 143. — The Mohawk Valley. 

Only when all the hills are worn down can the rivers rest 
from their labors ; and even then, if the lands are again 
uplifted, the rivers will at once dutifully resume their 
tasks. 

The broad valleys that well-established rivers carve for 
themselves in the lands are among the most attractive sites 
for human settlements. They are somewhat protected from 
inclement weather as compared to the adjoining uplands. 
They are floored with an abundant soil of fine texture. 
Their different parts are in easy communication with each 



224 PHYSICAL GEOGRAPHY. 

other. Many roads and railways take advantage of the 
low grades afforded by valleys that have been worn 
through mountain ridges. Indeed so well are man's needs 
supplied in fertile valleys, one might almost fancy that the 
valleys had been carved by their rivers for man's benefit. 
The truth is, however, that man often makes his home 
in valleys simply because he there finds more favorable 
surroundings than on the neighboring uplands. 

The Movement of Water Underground. 

Ground Water. — The water supplied by rain and snow 
is disposed of in part by evaporating from the surface, in 
part by running down the slopes of the land to the streams, 
and in part by sinking beneath the surface ; the last part 
is called ground water. 

The proportions of these several parts vary under dif- 
ferent conditions. The greater part of a light and long- 
continued rain may pass into ground water, especially if 
falling on a plain. A very heavy rain, or " cloud-burst," 
falling on strong slopes, is nearly all disposed of by direct 
run-off, causing sudden floods. 

When the ground is frozen, little water can enter it ; hence 
rivers rise in floods when deep snow is rapidly melted by a 
heavy rain. In arid regions a great part of the rainfall may 
dry off from the ground. 

When a region has been thoroughly dissected, steep slopes 
lead down to the streams. Then a large part of the rainfall 
is discharged by direct run-off, and the streams rapidly change 
in volume with every change from dry to wet weather. 

Ground water is essential to the growth of plants, whose 
roots must reach moist earth. Where grass and trees cover 



RIVERS AND VALLEYS. 



225 



the surface, much ground water taken in by their roots is 
discharged into the air by evaporation from their leaves. 

Loosely consolidated strata and deep rock waste take in 
much ground water. Firm rocks, such as granites, allow but 
little water to enter beneath the weathered waste on their 
surface. A region underlain by heavy strata of limestone (a 
comparatively soluble rock) may have many underground pas- 
sages dissolved along the rock crevices ; thus, nearly all the 
water may be .withdrawn from the surface. 

Caverns. — Caverns in limestone districts are the result 
of the solvent ac- 
tion of underground 
waters . The Mam- 
moth cave of Ken- 
tucky and the Luray 
cavern of Virginia 
are famous examples 
of this class. Streams 
gathering on the sur- 
face descend to underground passages by sink holes or 
swallow holes. After flowing underground for some dis- 
tance, they may issue in an enlarged and turbid current 
from the mouth of a cavern. 




Fig. 144. — Diagram of Cavern and Sink Hole. 



Several species of animals dwelling in the complete dark- 
ness of caverns are blind, but their senses of hearing and 
touch are highly developed. 

Where sink holes and cavern drainage prevail, so much 
water enters the ground that surface streams are compar- 
atively I'are. When the sink holes or the underground 



226 



PHYSICAL GEOGRAPHY. 



passages become obstructed, ponds and lakes are formed 
in the surface basins. 

The limestone uplands of Kentucky and Tennessee exhibit 
many of these features. The scarcity of surface water is 
often an inconvenience. Florida has numerous sink-hole 
ponds and lakes. The limestone uplands of Normandy in 
northwestern France have many valleys ending in sink holes. 




Fig. 145. — Natural Bridge, Syria. 



As denudation progresses, the roof of a cavern may fall in 
more or less completely. The beautiful Natural Bridge of 
Virginia is the remnant of a cavern roof. Fig. 145 gives a 
view of a natural bridge in Syria. 

Springs. — Very little ground water remains perma- 
nently beneath the land surface. Sooner or later, after 
descending to less or greater depths, it comes to the sur- 
face at a lower level than where it entered, emerging in 
the form of springs and joining the run-off of streams. 



BIVERS AND VALLEYS. 



227 




Fig. 146.— Diagra-m showing Distribntion of Ground 
Water (black). 



The movement of ground water is comparatively slow 
while percolating among the particles of rock waste or 
through the crevices of rocks. Where a large part of the 
rainfall enters the ground, the volume of the streams fed 
by springs is less variable than where the rainfall is mostly 
discharged by direct run-off during and shortly after a storm. 

Ground vv^ater slowly moves from hills and slopes, 
descending to lower 
levels and accumu- 
lating beneath the 
lower ground. It 
may, therefore, be 
generally found near 
the surface in val- 
leys, where the soil 
is usually damp. At the base of a slope, the ground water 
may issue in a spring, supplying a small brook. Innu- 
merable small springs occur unnoticed in the banks of 
streams, increasing their volume. 

In regions of sufficient rainfall and moderate relief, the 
ground water may be reached at almost any point except 
hill-tops by sinking wells to a depth of from 10 to 40 feet. 
The bottom of the well should be a few feet deeper than the 
level at which the trickling stream of ground water enters 
it from the crevice, so as to accumulate water in sufficient 
volume to supply ordinary domestic uses. 

Ground water and spring water carry very little rock 
waste (unless in solution), and are generally clear and 
pure. For this reason wells and springs generally afford 
a better water supply than the surface streams that receive 
the wash of fields and meadows. 



228 PHYSICAL GEOGRAPHY. 

In coastal regions ground water may flow forth as 
springs directly into the sea, either on a sloping beach 
near low-tide level, or at the bottom off-shore ; there they 
sometimes have a current so abundant as to supply a col- 
umn of fresh water that ascends through the heavier salt 
water to the surface. 

When a sloping coastal plain ends in a low bluff descend- 
ing to a beach, fresh water may generally be found by dig- 
ging a few feet beneath the base of the bluff. It is supplied by 
the slow-creeping sheet of ground water on its way to the sea. 

It is possible that feeble off-shore springs may rise into 
sea water of a temperature less than 32°. The spring water 
may then be frozen at the sea bottom. " Ground ice," some- 
times noticed by fishermen to rise from the shallow sea 
bottom in winter, may be thus explained. 

Artesian wells, or deep borings to water-bearing strata 
several hundred feet beneath the surface, are important 
sources of water supply in many regions. They have been 
described under coastal plains. It is essential that the water- 
bearing strata should reach the surface and receive their rain- 
fall at a higher level than that of the top of the well by which 
they are tapped. (See Fig. 78.) 

Charleston, Galveston, and many other coastal cities receive 
much water supply from artesian wells. In eastern Mary- 
land deep wells pierce strata that reach the surface and 
receive their rainfall west of Chesapeake Bay ; they lead the 
water beneath the nearly water-tight strata that floor the bay, 
and it is still fresh when rising in the wells. Southern Wis- 
consin and eastern Iowa have many artesian wells, supplied 
by water-bearing strata that slope gently away from the older 
land of northern Wisconsin. 

Hot and Mineral Springs. — Ground water sometimes 
descends deep beneath the surface, with a slow supply 



RIVERS AND VALLEYS. 



229 



from a large area, and then returns rather rapidly to the 
surface along a rock fracture. The water may then 
reach the surface in warm or hot springs, and bear an 
unusual amount of dissolved mineral substances. Such 
springs are frequently of medicinal value. 

Springs of this kind are associated with disturbed rock 
structures, as explained in con- 
nection with the tilted block ridges 
of Oregon. Saratoga Springs, 
N. Y., White Sulphur Springs, 
Va., Vichy in central France, and 
Karlsbad in Bohemia are examples 
of settlements determined chiefly 
or wholly by the value of their 
waters. These and many other 
mineral springs occur on or near 
lines of fracture in the earth's 
crust. 

Geysers. — In certain volcanic 
regions the temperature of the 
ground water may rise to or 
above the boiling point. Steam 
then issues with the water, often 
in a more or less explosive man- 
ner, and such steaming and 
spouting springs are called gey- 
sers. The geysers of Iceland have long been famous; 
those of the Yellowstone Park are now the most celebrated 
of the world. 

The intermittent action of many geysers suggests that a 
certain period of time (an hour or more) is necessary to warm 
the new supply of water that enters the crevice of discharge 




Fig. 147. —A Geyeer. 



230 PHYSICAL GEOGBAPHY. 

after a previous supply has been blown out by steam. In tlie 
deeper part of . the crevice the temperature of the boiling 
point is higher than at the surface, on account of the pres- 
sure of the water column. When the lower water readies its 
boiling point, a great part of it is quickly converted into 
steam, which blows the rest of the water out of the vent. 

RivEES AND Valleys. 

River Systems and their Parts. — A river is a stream of 
vrater bearing the waste of the land from higher to lower 
ground, and as a rule to the sea. A trunk stream and all 
the branches that join it constitute a river system. 

Stream is a general term, with little relation to size, Eill, 
rivulet, brook, and creek apply to streams of small or moder- 
ate size. River is generally applied to a trunk stream or to 
the larger branches of a river system. 

The land from which a river gathers its water and rock 
waste is called its basin. The crest line between the 
slopes leading to different streams or rivers is called a 
divide. 

On smooth plains and uplands there may be no noticeable 
crest line separating the side streams of neighboring rivers. 
Such surfaces may be described as tmdivided as to drainage. 
Undivided areas are often found on young plains and pla- 
teaus. When a plain or plateau is well dissected, numerous 
subdivides are developed, as on the Allegheny plateau. The 
rivers of vigorous mountains are sharply divided by the crest 
lines of the lofty ridges between the deeply eroded valleys. 
A worn-down region may have indistinct divides, as on the 
Piedmont district of Virginia or on the uplifted but not yet 
well-dissected plains of eastern Montana. 



BIVEBS AND VALLEYS. 



231 



Young Rivers. — The examples of land forms described 
in earlier chapters have shown that when ja, region is first 
raised from the sea, or when a former land surface is 
uplifted, tilted, or folded, the streams as a rule follow the 
lead of the land slopes, uniting here and there to form 
rivers of larger and larger size. 

Young rivers thus established proceed to cut down their 
channels where the slope is steep enough to give them an 




active current, by which the waste that they gather can be 
washed along ; but where the slope is faint, or where they 
enter a basin holding a lake, the streams lay down their 
load of waste and build up the surface. 

The coastal pampas of Buenos Ayres, Argentina, are nearly 
level, but contain slight depressions that hold water in the 
wet season, forming shallow lakes of small area. These 



232 PHYSICAL GEOGRAPHY. 

basins appear to be faint hollows in the original surface of 
the plain, not yet filled or drained. Their destruction is 
slow, for the rainfall is moderate, the plains are low and 
flat, and stream action is weak. 

The St. Lawrence system, with its many lakes, falls, 
and rapids, is a remarkable example of very immature 
drainage. The outlet of Lake Superior is by the Sault 
Sainte Marie (soo St. Mary). The outlet of Lake Erie is 
Niagara, with its renowned cataract and rapids. The out- 
let of Ontario is the St. Lawrence, with numerous rapids. 
The lakes favor navigation, but the rapids and falls obstruct 
it. Canals and locks have now been constructed, by which 
the rapids and falls are passed. 

The drainage of the highland of Canada between St. Law- 
rence river and Hudson bay bears every mark of youth. 
Lakes are very numerous and of irregular form. They 
often have several outlets, no one stream having cut down 
enough faster than the others to secure all the discharge. 
The streams are frequently interrupted by rapids or falls 
on rock ledges, in which channels are as yet cut only to 
moderate depth. The rivers frequently split into two or 
more channels, which reunite after wandering in independ- 
ent courses for 10 or 20 miles across country. 

This highland is a rugged, forested, and thinly populated 
wilderness without roads. All travel is by canoes along the 
water courses, and the canoes have to be carried past every 
rapid and fall. The birch tree, from whose bark portable 
canoes are made, is here as appropriate to the needs of the 
inhabitants as the camel is to the dwellers in arid deserts. 

The region of the great African lakes bears man}'" marks 
of youthful drainage. The lake basins here indicate a break- 
ing or warping of the earth's crust, like that in Arizona and 
southern Oregon. The adjacent plateaus are bordered by 



RIVERS AND VALLEYS. 233 

ragged fault cliffs. The Nile, flowing north from Lake Vic- 
toria Nyanza, and the Shire, flowing south from Lake Nyassa, 
are strong rivers of powerful current, descending over falls 
and rapids, very busy in the work of deepening their valleys 
and draining the lakes. 

By long-continued action the path of a river will in 
time be everywhere worn down or built up to such a slope 
that the current will be just strong enough to carry the 
load of waste that it receives. Such a river might be 
described as passing from youth to maturity. 

Lakes may be generally taken to indicate a youthful 
drainage system, as in the examples just given. In time 
they will be destroyed, partly by filling with the waste 
that is brought by the inflowing streams ; partly by the 
deepening of the outlet valley. Lakes should therefore 
be regarded as only temporary features in the long life of 
the river system to which they belong. The rivers may 
remain long after the lakes disappear. 

The distribution of lakes has already been considered in 
connection with various land forms. The plains of western 
Siberia and of Buenos Ayres possess lakes because they are 
young lands. The depressions between the tilted lava blocks 
of southern Oregon hold lakes because enough time has not 
yet passed to enable the streams to fill and drain their basins. 
Lava flows obstruct streams and for a time hold back lakes. 
Lakes of other kinds will be described later. 

As water stands nearly still in lakes, the arrangement 
of its layers depends on their temperature. Fresh water 
is densest at 39°. If warmed or cooled from this tem- 
perature, it expands and becomes less dense. In freezing 
it expands still more, and the ice floats buoyantly. 



234 PHYSICAL GEOGBAPHY. 

In warm climates the lowest temperature of a lake sur- 
face in the cool season determines the temperature that pre- 
vails in the deep water through the year. In cool or cold 
climates the deep water of large lakes is seldom colder 
than 39°. The surface layers may be colder than 39° in 
winter and warmer in summer. 

The surface water of a lake will not freeze over unless the 
whole water body can be reduced at least to 39°. Por this 
reason small lakes may freeze, while large lakes near by 
remain open through the winter. 

Lakes act as filters to the streams that enter them, 
decreasing their velocity and causing the stream-borne rock 
waste to settle ; thus deltas are formed at the inlets, and 
the lake bottom is strewn with fine waste or silt. 

Lake Geneva receives the turbid Rhone at its east end, 
where a large delta, 20 miles long, has grown a mile forward 
since Eoman times. The lake bottom is a plain- of fine silt. 
The Rhone at the outlet is wonderfully clear. 

Lakes act as regulators of the discharge of their outflow- 
ing rivers ; for the level of the lake changes little, whether 
the inflowing -streams are flooded or low ; and hence the 
outlet river has a relatively constant volume. 

The Ohio without lakes and the St. Lawrence with five 
great lakes are strongly contrasted in this respect. The 
latter has no great floods. The floods of the former may rise 
50 or 60 feet, spreading to 10 or 20 times the usual width of 
the river. 

Falls and Rapids. — It may sometimes happen that a 
breaking or bending of the land surface makes a slope 
steep enough to produce rapids or falls in the streams that 
run from the higher to the lower area. 



BIVERS AND VALLEYS. 



235 



It is probable that falls were formed in the Colorado Hiver 
at the points where it was crossed by the faults that sepa- 
rated the uplifted plateau blocks. These falls must have 
been rapidly worn away after each of the many slight move- 
ments by which the blocks were probably displaced. 

When a river is by any process turned across a new 
path, it falls dov^^n any descending slopes that occur on 
its course. Thus Niagara, v\^hen first taking its present 




Fig. 149. — Falls of the Tellowstone Eiver. 



course, fell over the blufC of the Niagara upland ; since 
then the fall has cut back a gorge about seven miles long. 
The larger or Canadian fall is now retreating two or three 
feet a year at its middle. 



The falls of the Yellowstone Eiver are of similar origin. 
They now occur at the head of a deep canyon cut by the river 
in the process of deepening its course. 



236 



PHYSICAL GEOGRAPHY. 



While a river is engaged in deepening its valley, it 
often flows from a stronger to a weaker rock structure. It 
will deepen the valley much more quickly in the latter 
than in the former, and a rapid or fall will be formed on 




Fig. 150. — Diagram of Torrent with Falls 
and Reaches. 



the slope produced between the two. Falls of this kind 
are numerous, especially in dissected plateaus and in lofty 
mountains. 

In passing from old-land rocks to the weak layers of a 
coastal plain a river develops rapids of moderate slope, as 
has already been explained. 

While the channel of a river is interrupted by many 
rapids and falls, it is more serviceable as a source of water 
power than as a waterway for large vessels. In the course 



RIVERS AND VALLEYS. 237 

of time the rapids and falls will be worn down to an even 
slope with the rest of the channel. A large river and its 
branches in this condition permit the entrance of river 
boats far inland. 

The falls in the lower course of the Kongo indicate an 
uplift of its basin so recent that even that great river has not 
yet been able to wear the falls away. The Kongo has there- 
fore been less available for exploration and commerce in 
Africa than the Amazon and the Mississippi have been in 
America. 

Graded Rivers. — A stream wears down its course on 
each weaker structure with reference to the next down- 
stream harder structure, as in Fig. 160. It thus comes 
to be divided into smooth reaches and plunging rapids or 
falls. Many rivers in New England are in this condition. 
The slope of a stream on a smooth reach is just sufficient 
to give it a velocity by which it can wash forward its load 
of waste. This part of the stream is then said to be 
graded. 

Rivers with reaches and falls furnish abundant water 
power for factories, and hence manufacturing cities grow 
up along them. Manchester, Lowell, and Lawrence on the 
Merrimac, Eochester on the Genesee, Minneapolis on the 
Mississippi, and many other cities are examples of this 
kind. 

When a river has been undisturbed by deformation of 
its basin for a long period of time, few falls remain to 
interrupt its course, and its graded reaches become longer 
and longer. It is in this well-established condition that 
many large rivers of the world are found. 



238 PHYSICAL GEOGRAPHY. 

In vigorous mountains, where many successive uplifts 
occur, even the large rivers are hardly able to grade their 
courses during the pauses between the uplifts ; the small 
branches are kept in a torrential condition. Only when 
the last uplift was long ago, as in subdued mountains, 
can the streams develop well-graded courses. 

It is only in streams where valleys are not yet graded that 
the observer may expect to see the stream at work deepening 
its valley. No such action is perceptible in graded streams. 

When a graded condition is reached in even the smaller 
streams, the slope will be steepest near the headwaters 
and least near the river mouth ; thus the profile of a well- 
developed river is a curve of decreasing slope from head 
to mouth. 

The large volume of the lower part of a river enables it to 
run rapidly even on a gentle slope. Its load is relatively 
fine-textured and easily carried, having been ground finer 
and finer while washing down from the upper valleys. 
Every thread of the river current does its part of the work 
of washing the load towards the sea. Under these favoring 
conditions a faint slope will enable the river to do its work. 

The small volume of a headwater stream permits friction 
with the banks and bed greatly to retard its current. The 
load that it receives from the valley slopes is relatively 
plentiful, coarse, and difficult to drag along. The only 
way in which a small stream can do its work under these 
unfavorable conditions is by maintaining a steep slope. 

A swift headwater stream ordinarily has so little fine 
waste to carry that its water is clear ; the coarser waste is 
dragged along its bed. Only at a time of flood does it become 
turbid. The slow-moving waters in the lower course of a 
flat-graded river gather so much fine silt that they are nearly 



BIVERS AND VALLEYS. 239 

always somewhat turbid from suspended and slowly settling 
sediments. 

Water moves so easily that large rivers assume very faint 
slopes ; the lower Mississippi has a descent of only 2 or 
3 inches to the mile, yet it bears along a vast amount of 
rock waste : 6700 million cubic feet of suspended silt, 750 
million of silt dragged along the bottom, and 1400 million 
of mineral substances in solution every year. 

When a river system is found to possess graded valley 
floors extending without break far up toward the heads of 
its many branches, it must be concluded that the streams 
have long been at work to produce so remarkable an 
adjustment between volume, load, and slope. This beau- 
tiful adjustment is one of the best proofs that valleys are 
carved by the streams that drain them ; for by no other 
process could the adjustment be produced. 

The Development of Valleys. — While a young river is 
deepening its valley, the valley sides are steep and the 
valley bottom is no wider than the river channel. At 
such a time the valley floor offers no attraction to settle- 
ment, as it affords no level ground for roads or villages 
near the river ; if built in such a valley, they must perch 
on the side slope. If the valley is deep, it may act as a 
barrier between the uplands on either side. 

The dissected plateau known as the Mesa de Maya in 
southern Colorado, fronting the Rocky mountains, affords 
many examples of narrow young valleys in their relatively 
inaccessible and unattractive stage. 

Floods have little room to spread in a steep-sided valley ; 
hence they rise rapidly on the valley walls, even 30 to 50 feet 
in a day or two. Thus hemmed in a valley, the flood flows 



240 



PHYSICAL GEOGRAPHY. 



rapidly and sweeps away all obstacles, gradually subsiding as 
its supply of water lessens. 

It is for this reason difficult to maintain road bridges across 
the streams of the Allegheny plateau ; the great expense of 
building strong and high bridges cannot be borne by the scat- 
tered population. The streams are therefore commonly crossed 
by fording. At time of high water, travel is interrupted. 

Thus far it has been implied that an active stream cuts 
its channel directly downward and not at all sideways. 

But at every bend a 



stream tends to cut more 
on the outer than on the 
inner bank; hence as it 
cuts down it also cuts 
outward. 

A perfectly straight 
stream might cut verti- 
cally downward. As the 
valley sides wasted, the 
valley would become wider 
at the top, but not at the 
bottom, as in Fig, 151 
(a, b, c). 

If no wasting of the 
walls occurred, the trench 

Fig. ISl.-Diagram of a straight VaUey. Q^f^ ]jj g, crOOkcd Stream 

would slant outward at every turn, as in Fig. 152 (a). This 
is sometimes seen to a slight degree in narrow gorges or 
chasms, for the fastest current is not in mid-channel, but 
runs near the outside of every turn ; hence there is more 
wearing on the outer than on the inner side of the stream. 
The valley walls waste while the trench deepens. When 
grade is reached, the walls will have flared open ; but they 




RIVERS AND VALLEYS. 



241 



will be steep on the out- 
side of every curve where 
the stream has under-cut 
the valley wall, as in Fig. 
152 (b). Unsymmetrical 
valley sides are formed in 
this way ; sloping spurs 
enter each curve opposite 
cliff-like bluffs, and the 
belt of country occupied 
by the turns of the river 
is broader than at first. 

The Development of 
Meanders. — When a 
rivei" has graded, its val- 
ley, it almost ceases to 
cut dov^^nward, but it may- 
still wear on the outer 
bank of every turn, and 
thus contmue to broaden 
the belt that its valley 
floor occupies. At the 
same time the turns tend 
to become smooth curves 
of regular form, better 
adapted to the regular 
movement of the river. 

- As- the outer bank of 
a curving channel is cut 
away, the inner bank is 
filled up to flood level 
with rock waste from 




Fig. 152. — Diagrams of a Crooked Eiver widening 
its Valley, 



242 



PHYSICAL GEOGRAPHY. 



further up stream. A strip of flood plain is thus developed 
on the inner side of each curve, as in Fig. 152 (c); first 
on one side and then on the other side of the river. 

The north branch of the Susquehanna follows a deep and 
winding valley through the Allegheny plateau in northern 
Pennsylvania. It has begun to develop strips of flood plain 
at the base of its sloping spurs ; steep cliffs rise above the 
opposite river bank. The Osage river has worn an extremely 

crooked valley in the 
uplands of central Mis- 
souri, and it is just be- 
ginning to form narrow 
strips of flood plain. 



With continued ac- 
tion the river con- 
sumes more and more 
of the spurs that enter 
its cui'ved course, as 
in Fig. 152 (^,e). In 
time it obliterates 
them, as in Fig. 152 
(/). Then an open 
flood plain is formed on which the river takes such a 
curved course as suits its volume, with only occasional 
constraint by tlie valley walls. The narrower the original 
belt of turning, the narrower the flood plain at this stage 
of development. 

The lower Missouri has a valley floor about as broad as its 
belt of curves. Villages grow on the uplands above points 
where the river flows against the valley walls. The valley 




Fig. 153. — Contour Map of the Missouri River Valley. 



BIVJEES AND VALLEYS. 243 

of the Ohio above Cincinnati now retains only the blunt 
remnants of the spurs that once entered its turns. 

If a stream has a large load of coarse rock waste, its 
graded flood plain must be relatively steep (a descent of 
from 5 to 20 feet or more a mile). In this case the stream 
does not turn far aside from a direct course along the flood 
plain; but it is constantly embarrassed by the formation 
of bars and islands of gravel and sand, splitting its current 
into many shifting channels. 

The Platte, fed by branches rising in the Rocky mountains 
and gaining much waste from the weak strata of the Great 
Plains, requires so steep a slope that it cannot cut a deep 
valley, although the Plains in the upper part of its course are 
high above baselevel. The river is like a braided network 
of many channels. ' Many rivers flowing from the Alps to the 
lower surrounding country are of this kind ; gravel bars and 
islands lie between their divided channels. 

If the waste borne by a river is of very fine texture, the 
flood plain will have a very gentle grade, and the valley 
^will be cut down close to sea level. The slope down the 
valley is then so faint that the river easily turns aside from 
a direct course on its broadened flood plain, and in this 
way (whatever its original course) develops a system of 
serpentine curves or meanders, as in Fig. 152 («,/). 

The Meander, a serpentine river of Asiatic Turkey, has 
given name to this river habit. 

On a nearly level flood plain any accidental obstacle may 
divert a stream from a direct course and turn its current 
toward one bank or the other. Thus turned, its wandering 
will be increased by constantly cutting away its outer bank. 



244 



PHYSICAL GEOGRAPHY. 



Even if nearly straight in the beginning, it must come to 
meander on a flat flood plain. 

The size of the meanders increases with the volume of the 
stream. A meadow 
brook may swing 
around curves meas- 
uring only 40 or 50 
feet across. The 
curves of the lower 
Mississippi are from 
3 to 6 miles across. 
The flatter the flood 
plain, the greater the 
arc of the meander 
turning. The Koros 
(Fig. 154), on the Plain of Hungary, has its meanders remark- 
ably developed. 




Fig. 154. — A Meandering Kiver on the Plain of Hungary. 



Broad Valleys. — Wherever a meandering river swings 
against its valley walls, they will be slowly consumed. 
As the meanders slowly change their course through the 
flood plain (Fig. 152, e, /), cutting away the valley walls 
now here, now there, the flood plain gradually becomes 
wider than the meander belt. 

The Mississippi below Cairo has opened a flood plain from 
20 to 60 miles wide, that is, five or more times wider than its 
meander belt. Being a river of great volume, it has rapidly 
advanced to a thoroughly mature stage of development, while 
its small branches on each side are still young. 

Many ISTew England streams meander on the flood-plained 
reaches between their falls. 



In the fine rock waste of a broad and flat flood plain, 
a large river changes its course rapidly, taking material 



BIVEES AND VALLEYS. 



245 



from the outer banks, where its current is strong, and 
depositing it further down stream on the inner banks, 
where its current is weaker. 

The breadth of the meander belt would in time become 
excessive, if the necks of the flood-plain spurs between 
adjoining meanders were not gradually narrowed and cut 
through, the meander around the spur being then deserted 
for a shorter and straighter course. 

Large rivers, like the Mississippi, exhibit all stages of 
this process. An abandoned 
meander is occupied by nearly 
stagnant water, more or less 
completely separated from 
the new and shorter channel 
by deposits of silt in the ends 
of its arms ; in time it becomes 
an ox-bow lake. A group of 
well-developed meanders may 
be transformed into a com- 
paratively straight stretch, 
with abandoned meanders and 
ox-bow lakes on each side. 

A continuous and deep 
channel is maintained by a 
river near the outer bank of 
a meander, but on the straighter stretches between two mean- 
ders the channel is irregular and variable, being clogged with 
many shifting bars and shoals. It is in these parts that the 
navigation of a meandering river like the Mississippi is diffi- 
cult. 

When a valley floor is old enough to be widened and 
when its walls are worn back to gentle slopes, it becomes 
much more available for human uses than when young, 




Fig. 155. — Meanders of the Mississippi. 



246 PHYSICAL GEOGRAPHY. 

narrow, and steep-walled ; but its flood plain is exposed to 
invasion by tbe shifting cbannel, and to overflow at time 
of high Avater. 

The shifting of the channel may be checked by ]irotect- 
ing the outer bank with stone or wood work, but this is 
expensive. Eising floods may be held back by dikes or 
levees built on the plain a little distance from the river 
banks. When the levees are overtopped or breached, wide- 
spread floods may result, such as occurred on the Mississippi 
flood plain in April, 1897, when about 14,000 square miles of 
the plain (two-fifths of the entire area) were under water. 
The value of live stock and crops lost in this flood was esti- 
mated at $15,000,000 ; many thousand people were for a 
time driven from their homes. 

In March. 1890, a strong flood in the lower Mississippi 
broke through the levees on the left bank, forming the ■'■' isita 
crevasse " (a break on the Nita plantation), flooding the plain, 
carrying river silt into the shallow waters of the Gulf, and 
ruining the oyster beds east of the delta. 

Shifting of Divides. — While a river is wearing down 
its valley to a smooth grade, ravines are worn into the 
valley sides. The ravines gradually lengthen headwards 
and dissect the upland surface. As their size increases 
they may be called branch valleys. 

Many of the great ravines in the walls of the canyon of the 
Colorado are of this origin. Most of the branch valleys of 
dissected coastal plains, as in South Carolina, and of plateaus, 
as in West Virginia, are formed in this way. 

The headward growth of branch valleys is more rapid in 
weak than in strong rock structures. It sometimes happens 
that a branch valley gnaws its way headward along a belt 



RIVERS AND VALLEYS. 



247 




Fig. 156 a. — Diagram of a Shifting Divide (first stage). 



of weak rocks ( Tf, Fig. 156), from the deep-cut valleys of a 
large river (i?), and taps the side of a smaller river (aS'), 
whose valley is not 
cut so deep. The 
upper waters of the 
smaller river are then 
turned to the large 
river, and the lower 
course [D) of the 
smaller river is left 
in diminished vol- 
ume. As this change 
progresses, the divide 
is shifted from its or- 
iginal position {AB) 
and in time takes a 
position {AC) across 
the smaller valley 
above the beheaded 
stream {B). Still 
further changes may 
occur later. 




Fig. 156 6. — Diagram of a Shifting Divide (second stage). 




The arrangement of 
streams on belted 
coastal plains may be 
explained as the result 
of shifted divides. At 
first the rivers that are 

extended from the older land across the young coastal plain 
follow independent courses to the sea. Branch valleys grow 
out from the several rivers along the belt of weaker strata 
on which the inner lowland is to be worn. A branch stream 



Fig. 156 c— Diagram of a Shifting Divide (third stage). 



248 



PHYSICAL GEOGRAPHY. 




Fig. 158. —Diagram of Rearranged Kiver Courses. 



EIVERS AND VALLEYS. 



249 



:N0RTH CAROLINA 




Fig. 159. — Boundary of Georgia and South Carolina. 



(-E, Fig. 157) of the largest river (A) lias the advantage of 

the greater depth to which the main valley is worn ; in time 

it captures one after the other of the smaller streams (B, C, D) 

and leads them along the 

inner lowland to the main 

river, leaving their lower 

courses (F, G, Fig. 158) 

beheaded. 

The western angle of 

South Carolina marks the 

place where the former 

upper waters of the Chat- 
tahoochee river have been 

captured by a branch of 

the Savannah river. In 

this case the advantage 

enjoyed by the Savannah 

resulted from its shorter 

course to the sea, in consequence of which its headwaters 

were enabled to erode 
their valleys deeper 
than the valley of 
the Chattahoochee. A 
state boundary has 
thus been determined. 
• Further beheading of 
the Chattahoochee by 
the Oconee may take 
place in the future. 

The city of Toul in 
eastern France stands 
at a sharp turn in the 
Moselle river, where 
its upper waters have 
been captured from 

Fig. 160 — Outline Map of Eastern France and Western ^ 

Germany. the MeUSC, tO whlch 




250 



PHYSICAL GEOGRAPHY. 



they once belonged. Another branch of the Meuse has been 
captured by the Aisne, a member of the Seine system. . Here 
the captures seem to have taken place because the Meuse was 

delayed in deepening 
its valley on account 
of having to cut a 
deep gorge in the hard 
rocks of the Ardennes 
highlands, further 
down stream. As a 
consequence the small 
meanders of the di- 
minished Meuse no 
longer fit the larger 
meanders of its 
swinging valley, as 
shown in Fig. 161. 



Mature Rivers. — 
When a river and 
its larger branches 
have destroyed tlieir 
lakes and falls and reduced their valleys to graded slopes ; 
when the larger streams have broadened their valley floors 
so that they can meander freely upon them in curves 
appropriate to their volume ; and when the growth of 
branch streams has shifted the divides so far that no fur- 
ther changes of importance are to be expected, the river 
system has reached the mature stage of its development. 

A river system occupies so large a region that it cannot be 
easily pictured in the mind ; but as its different parts are 
patiently studied, and as an understanding of their wonderful 
relations is gradually gained, the system as a whole may be 




Fig. 161. 



-Irregular Course of the Meuse in its Meandering 
VaUey. 



RIVERS AND VALLEYS. 251 

conceived. It will then be seen to be almost as marvellous 
as any organic forms in its well-ordered arrangement of parts 
and in their survival by reason of natural selection. 

Mature rivers accomplisli the drainage of their basins 
and the transportation of rock waste to the sea in the most 
active and perfect manner. There remain no undivided 
uplands from which a great part of the rainfall may be 
returned to the atmosphere by evaporation. The largest 
possible share of the rainfall is shed from the well-carved 
surface of the land, and runs off in the streams with no 
lingering delay in lakes or undue haste in falls. No 
hard rock ledges remain in the lower courses to delay the 
deepening of the upper valleys. Everywhere the waste of 
the land is washed down the slopes to the streams, and 
delivered in such quantity that the streams are kept work- 
ing at their full capacity to transport the waste toward 
the sea. 

Old Rivers. — If no disturbance occurs, a maturely 
developed river system passes by slow degrees into a 
quiet old age. The hills waste away to fainter slopes and 
yield less and less waste to the streams. The texture of 
the waste becomes finer and finer. More of the waste is 
carried in solution. As the work of carrying the waste is 
thus made more easy, the meandering streams very slowly 
wear their flood plains to gentler slopes, and in this way 
always maintain a nice adjustment between their ability 
to do work and the work that they have to do. 

The extreme old age of a river system would be character- 
ized by low and ill-defined divides between faint slopes lead- 
ing to broad flood plains, on which the streams would meander 



252 PHYSICAL GEOGRAPHY. 

with great freedom. An increasing share of the transported 
"waste would be dissolved. A large amount of rainfall would 
be lost by evaporation on the gentle slopes. 

It is unusual to find an old river system. Tlie lower 
trunks of large river systems often gain very gentle slopes 
and free-swinging meanders, but before a correspondingly 
advanced development is attained by all the small side 
branches and the headwaters, movements of elevation or 
depression generally occur with more or less tilting and break- 
ing ; and in this way the rivers are made young again and set 
to work at new tasks. 

Revived Rivers. — At any stage of development the 
region drained by a river may be uplifted to a greater 
height above sea level. Then the river will at once begin 
to cut its valley floor down to grade with respect to the 
new baselevel. The renewed activity of such rivers sug- 
gests that they should be called revived. One of the 
first effects of revival and renewed dissection is to bring- 
to life again the falls that had been worn down before the 
region was uplifted. 

The Great Ealls of the Missouri in eastern Montana occur 
in a young valley, where the revived river is dissecting the 
worn-down plains, now uplifted. jSTo falls could have existed 
during the old age of the river, when it flowed across the 
worn-down plains. The water power of the revived falls now 
determines the site of the growing city of Great Falls, with 
its important industrial works. 

A common effect of revival is the erosion of a narrow 
trench in the floor of a mature, well-opened valley. The 
gorge of the Rhine, already described (Fig. 119), is an 
example of this kind. 



RIVERS AND VALLEYS. 



253 



Kootenai river in the Rocky mountains of northern Mon- 
tana, and. Fraser river in the mountains of British Columbia, 
botli exhibit this combination of mature and young features. 
The railroad that follows each valley is located on the former 
valley floor, which now appears as a rock bench or terrace 
above the present gorge. 

Old rivers flowing across low worn-down mountains are 
rare, but revived rivers flowing through gorges in uplifted 
lowlands of this kind are common. The rivers of the 
Piedmont district of Virginia (Fig. 116) are thus explained. 



Entrenched Meanders. — If uplift permits a mature or 
. old meandering river to entrench itself beneath its former 
flood plain, its new valley will be regularly curved, instead 
of irregularly crooked, as in its first youth. The meander 
belt will be somewhat broadened as its curves are cut 
down, for the river will cut outward as well as downward 
at every turn. 

The lower Seine in northwest France affords a beautiful 
example of a narrow valley of regular serpentine curvature, 
entrenched in the upland 
(a worn-down plain, up- 
lifted) of l^ormandy. 
Above the reach of strong 
tide, spurs of the upland 
enter every loop of the 
river. Nearer the mouth, 
where rapid tidal currents 
aid the action of the river, 
the spurs of the upland 
are almost obliterated, and the flood plain is broader. 

The regular curves of the north branch of the Susquehanna 
have probably been developed after the uplift of the worn- 
down plain on ^hich the river formerly meandered. 




Fig. 162. — Diagram of a Narrowed Spur. 



254 



PHYSICAL GEOGBAPHY. 




It sometimes happens that a revived river may wear through 

the neck of one of the up- 
land spurs that enter its 
trenched course, and then 
desert a roundabout course 
for a more direct one (Figs. 
162, 163). Eapids will 
occur for a time at the 
cut-off. The village of 
Lauffen (Eapids), on the 

Fig. 163. — Diagram of Cut-Off Spur. . ^ '^ 

JSTeckar m south Germany, 
gains water power from rapids of this kind. The former 
course of the river is seen 
in a meadow beautifully 
curved around an isolated 
hill, the cut-off end of an 
upland spur (Fig. 164). 

The Moselle in western 
Germany (Fig. 160), sink- 
ing its course in an uplifted 
old-mountain plateau, has 
a number of deeply incised 
meanders (Fig. 165). In- 
cised meanders and cut-off 
spurs occur on the Alle- 
gheny river above Pitts- 
burg. Railroads following 
an.incised meandering val- 
ley often tunnel through 
the narrow necks of the 
spurs, thus anticipating 
the behavior of the river 

by many centuries. Fig. lei.— Entrenched Meanders of the Neckar. 

Lengthwise and Crosswise Valleys. — Revived rivers 
give a simple explanation of the origin of certain length- 




BIVERS AND VALLEYS. 



255 



wise and crosswise valleys. The former are often broad 
lowlands with a deep soil weathered on weak underlying 
rocks. The latter are 
steep-sided gorges 
cut in rugged, hard- 
rock ridges or high- 
lands. 

For example, the 
Delaware river gath- 
ers many branches 
from the open inner 
valleys of northeast- 
ern Pennsylvania, 
and escapes by a deep, 
narrow notch, called 
the Delaware Water- 
gap, in Kittatinny 
mountain, at the 
northwestern corner 
of New Jersey. 

In such cases the 
rivers had their pres- 
ent arrangement be- 
fore the valleys were 
excavated, when the 
whole region stood 
lower than now and a broad lowland spread far and wide 
at about the level of the ridge crests and highland sum- 
mits of to-day, as in Fig. 166. After the elevation of the 
region, all the revived rivers began to wear down their 
valleys. No branch stream could cut down faster or 
deeper than the larger river that it enters. The inner 




Fig. 165. — Entrenched Meanders of the Moselle. 



256 



PHYSICAL GEOGRAPHY. 




lengthwise streams could not deepen tlieir valleys faster 
than the crosswise valley was deepened by the trunk river. 

But the inner valleys 
widen with relative 
rapidity on their weak 
rocks, and in time 
become broad open 
lowlands, while the 
outlet valley still 

Fig. 166. — Transverse and Longitudinal streams. vetaiTlS f\ O'OT'P'P-like 

form in the resistant rocks which now stand up as a ridge 
or belt of highlands, 
as in Fig. 167. 



This explanation 
applies to the Susque- 
hanna, cutting gaps in 
the Allegheny ridges, 
and to the Potomac, 

cutting a deep passage ^'S. 167. -Transverse and Longitudinal Valleys. 

in the Blue Eidge at Harpers Ferry, and draining the length- 
wise Shenandoah valley in Virginia (Fig. 117). 




Lakes in Warped Valleys. — In regions of relatively 
active disturbance, like vigorous and growing mountain 
ranges, the movements of the earth's crust may warp or 
deform the surface so that one part of a valley is depressed 
and another, further down stream, is elevated. A lake 
will then be formed in the depressed part of the valley. 

The basins of the larger lakes around the Alps are best 
explained as warped valleys. Some of them are so deep that 
the bottoms lie below sea level. In all examples of this kind 



RIVERS AND VALLEYS. 



257 



the lake must be regarded as short-lived compared to the 
mountains around it. The inflowing streams form deltas at 




Fig. 168. — Watergap of the Susquehanna in North Mountain, Pennsylvania. 

the shore, and furnish fine silt with which the bottom is 
strewn. The outflowing river cuts down its valley, and 
lowers the level of the lake. In a short time, compared to 




Fig. 169. — Contour Map of the Susquehanna Watergap in North Mountain, Pennsylvania. 



258 PHYSICAL GEOGRAPHY. 

the life of the mountains, the lake will be destroyed, and the 
river will resume its steady flow. 

Antecedent Rivers. — At any stage in the history of a 
river a tilting or uplifting movement of the earth's crust 
may tend to reverse the slope of a part of its valley. If 
the movement is too rapid for the river to overcome, its 
current will be turned away to a new path, following the 
slope of the uplifted surface. 

This is usually the case, as has been shown in the moun- 
tains of Oregon and Nevada, in the Black Hills dome, and in 
the Jura arches. In lofty mountains of vigorous growth the 
main range is usually the divide between river systems that 
flow away to the lowlands on each side. 

It may, however, sometimes happen that a large river is 
powerful enough to maintain its path by cutting down the 
uplifted part of its valley, and then it will not be displaced. 
As such a river existed antecedent to the disturbance of 
its basin, it may be called an antecedent river. 

The Kanawha river has preserved its course through the 
plateau of West Virginia in spite of the uplift by which the 
plateau was raised 1000 feet more than the upper part of 
the river was in Virginia and North Carolina. 

Great rivers, like the Sutlej, gathered in the inner 
valleys of the Himalaya and escaping to the plains of 
northern India by "deep gorges, have maintained their 
courses through the marginal ridges which have been 
uplifted and added to the mountain system in a compara- 
tively late stage of its history. 



EI VERS AND VALLEYS. 259 

These rivers may therefore be called antecedent to the 
marginal ridges. They have cut their outlet valleys down 
as the ridges were upraised, much in the way that a circular 
saw cuts its way through a log that is driven against it. 

Before the last uplift of the plateau-like Slate mountains 
(Fig. 119), now trenched by the middle Rhine, the river fol- 
lowed its present path, as is shown by the trough in which the 
young gorge is cut. It therefore appears to have maintained 
its course in spite of an uplift across its path. It is an 
antecedent river in this part of its length. 

Engrafted Rivers. — When a region near the sea is 
uplifted and a submerged continental shelf is laid bare as 
a coastal plain, the rivers of the older land are extended 
across it. It sometimes happens that several extended 
rivers unite on their way to the sea, thus grafting upon 
one trunk a number of previously independent river 
systems. It is chiefly in this way that the greater 
river systems of the world have reached their immense 
development. 

The uplift of the coastal plain that borders the Gulf of 
Mexico has engrafted the White, Arkansas, Eed, and Tennes- 
see rivers on the extended trunk of the Mississippi, whose 
total drainage area now measures over 1,240,000 square miles. 

By similar grafting the great rivers of Brazil have been 
united with the lower trunk of the Amazon, giving it a basin 
of 2,500,000 square miles. A further uplift would probably 
make the Tocantins a regular member of the same system, to 
which it is now imperfectly attached. 

When large engrafted rivers grade their courses (and 
this they do almost as fast as the new land is raised before 
them), they become of importance as navigable waterways, 



260 



PHYSICAL GEOGRAPHY. 



reaching far into the interior of their basin. The navi- 
gable rivers of the ^Nlississij^pi and Amazon systems 
measure many thousand miles in length. 

Dismembered Rivers. — When the sea advances on a 
depressed region, the lower valley of a river system may 

be submerged, forming an 
estuar}* or bay. and leav- 
ing the river branches to 
enter the sea as independ- 
ent river systems. The 
entrance of navigable 
arms of the sea far into 
the lands nmj compen- 
sate more or less full}- for 
the drowning of the lower 
varley floors, as in the 
case of the St. Lawrence. 



The small rivers that 
enter Xarragansett bay, 
E. I., f orined branches, be- 
fore submergence, of what 
may be called the Narra- 

Fig. 170. -Map of Narragansett Bay. ganSCtt river SyStcm. All 

the rivers of eastern Virginia and inner Maryland were 
once united in a trunk river that flowed across what is now 
part of the continental shelf, before its larger valleys were 
drowned to form Chesapeake bay and the Potomac estuary 
(Fig. 117). 




A T L A 



Example for Review. — The Hudson river drains a broad 
interior valley, a part of the great lengthwise valley of the 



RIVERS AND VALLEYS. 



26] 



Appalachian mountain belt, occupied by farms all along 
its extent. At Newburgh the river leaves the broad 
valley and enters a deep steep-sided gorge in its famous 
passage through the Highlands of southeastern New York, 
an extension of the uplifted old-mountain plateau of 
southern New Enpiand. 




Fig. 171. — The Hudson River, looking North from West Point. 

The difference in the dimensions of the broad and narrow 
parts of the Hudson valley is an indication of the difference 
in the ability of the underlying rocks to resist weathering. 
The broad lengthwise valley was worn down no faster than 
"the narrow crosswise gorge through which it is drained ; 
but it widened much faster than the gorge because its rocks 
are weaker than those of the Highlands. The waste from 
the broad valley drained by the Hudson has been carried, 
grain by grain, through the narrow gorge. 

The large volume of the Hudson below Albany is due, 
not to the rainfall on its basin, but to a moderate depres- 
sion of the valley bottom beneath sea level, whereby it has 
been drowned to a navigable depth. The former prolon- 



262 PHYSICAL GEOGRAPHY. 

gation of the valley, excavated across the continental shelf 
when the region stood higher, has been traced by sound- 
ings for more than 100 miles off shore. The navigable 
waters now entering through the Highlands have been of 
great commercial advantage to New York city, whose 
history must have been very different if the Hudson has 
been as shallow in the Highland gorge as the Potomac is 
in its gorge through the Blue Ridge below Harpers Ferry. 

The lower branches of the Hudson are, strictly speaking, 
independent rivers, now dismembered by the submergence of 
the valley that was excavated by the trunk river of the system 
to which they once belonged. 



CHAPTER X. 
THE WASTE OF THE LAND. 

Comparison of Waste Streams and Water Streams. 

Much attention is given to the forms assumed by the 
waters that flow from the lands to the sea. Surface and 
ground water, springs, brooks, and rivers, falls and lakes 
have thus been treated. A good share of attention should 
also be given to the forms assumed by the waste of the 
land on the way to the sea, from their beginning in the 
layers of soil produced by the weathering of the rocky 
structures of the earth's crust to their end in layers of 
sediment spread upon the sea floor. 

The movement of land waste is generally so slow that 
it is not noticed. But when one has learned that many 
land forms result from the removal of more or less waste, 
the reality and the importance of the movement are better 
understood. It is then possible to picture in the imagi- 
nation a slow washing and creeping of the waste down the 
land slopes ; not bodily or hastily, but grain by grain, 
inch by inch ; yet so patiently that in the course of ages 
even mountains may be laid low. 

There are many resemblances between the movement of 
water streams and of waste streams. Water flows along 
stream and river channels, more rapidly at the surface, 
more slowly at the bottom ; it is here delayed in lakes, 
there hurried down rapids. Land waste may be thought 



264 



PHYSICAL GEOGRAPHY. 



of as moving in streams and sheets down every hillside 
and along every valley, more rapidly at the surface of the 
ground, more slowly at a depth of several feet ; more 




Fig. 172— Rock Waste on Mountain Slopes. 



rapidly on steeper slopes, more slowly on plains. The 
shape of the land surface and its usefulness as a home 
for man depend in no small degree on the character of 
the sheet of waste with which it is clothed. 



THE WASTE OF THE LAND. 265 

Flowing streams of water are valuable in many ways, as 
affording water supply, water power, and water transpor- 
tation. Creeping sheets and streams of waste are of even 
greater value, for upon their surface the most useful plants 




(lIlLmi. 'J_L/ VlAiiklL "Uih'iAgffJ\1l)lMi'iiftfl(';, iili'i 



Fi' 173 — ^ LaL- "^loo'- Plain 



grow, and upon plants all the higher forms of animal life 
depend, directly or indirectly, for food. Many human 
industries and arts are dependent upon the plants that 
grow upon the slow-moving sheets and streams of waste. 

The Forms Assumed by the Waste of the Land 
ON THE Way to the Sea. 

The Formation of Soil. — The decay of the rock crust 
of the earth under the attack of the weather has already 
been described as a characteristic of the lands. Nearly all 
parts of the land would be covered with a sheet of waste 
many feet deep, and bare ledges would be almost unknown, 
if it were not for the movement of the waste after it has 
been loosened. 

Many processes aid in the production of rock waste. 
Changes of temperature through day and night, in summer 



266 PHYSICAL GEOGRAPHY. 

and winter, cause small movements in solid rock, and aid in 
opening minute fractures near the surface. Water in rock 
crevices expands as it freezes, and thus helps to wedge apart 
adjacent blocks. 

Most rocks suffer chemical changes under the action of 
water and air, and as a rule these changes aid decay and 
crumbling. The changes may go on as deep beneath the sur- 
face as water and air can penetrate. They are delayed or 
stopped when the ground water is frozen or wanting. They are 
aided when the ground water carries down with it the products 
of decomposing vegetation from the surface. Hence deep rock 
decay is less active in frigid or arid than in moist torrid climates. 

Where the land surface is well covered with its own 
waste, a quarry {Fig. 59) or railroad cut may exhibit the 
gradual change from the solid rock beneath to the fine 
waste at the surface. While the rock is only divided into 
large blocks by fine cracks or joints here and there, a 
cubic inch of waste at the surface may be subdivided into 
millions of minute particles. If plants have long grown on 
the waste, it is darker near the surface than below, and the 
darker part is then commonly called soil. 

Soil is generally understood as including a share of vege- 
table matter with rock waste, but some soils contain no 
vegetable matter. 

Some rocks may be slowly dissolved by water. Limestone 
is the most important of these, and the origin of sinks and 
caverns by solution has already been described. As the lime- 
stone weathers and the soluble parts are slowly carried away, 
much of the insoluble parts of the rock remain ; thus it may 
happen that a blue limestone is covered with rusty clay waste. 
A foot of the clay may represent 10 or 20 feet of rock. If the 
clay is stripped off, the limestone is sometimes found etched 
into curious irregular forms. 



THE WASTE OF THE LAND. 267 

Where rock waste is formed on a slope, its finer particles 
at the surface are washed down a little by the run-off of 
every rain. Besides this the whole mass slowly creeps 
down the slope, advancing faster at the surface and more 
and more slowly beneath. 

Every change of condition between cold and warm, dry and 
wet, melted and frozen, that causes a gain .or loss of volume 
in the rock waste aids its slow movement down hill. With 
countless minute changes, every particle is led, slowly but 
surely, from higher to lower ground. 

The growth and decay of plant roots aid the downward 
creeping of the waste. Earthworms, ants, and various bur- 
rowing animals bring the smaller particles of waste to the 
surface, and thus promote weathering and washing. 

All causes of movement are greatest near the surface ; 
hence the outer part of the waste sheet moves faster than 
the under part. As gravity is more effective on steep than 
on flat surfaces, the waste creeps faster on hillsides than on 
nearly level plains. In both these respects waste streams 
resemble water streams. 

On surfaces of very gentle slope, such as plains of 
moderate relief, the waste is removed so slowly that it 
becomes unusually deep. The deeper the sheet of waste 
becomes, the less active is the attack of the weather on the 
under rock, and the slower the waste increases in depth. 
The surface particles become finer and finer the longer 
they are exposed; the finer they are, the more easily they 
wash and creep away. In this way a balance may be 
struck between slow removal at the surface and slow 
production at the base of the waste. 

It thus appears that plains favor human occupation, not 
only because they may be easily traversed, but also because 



268 PHYSICAL GEOGRAPHY. 

they usually possess a fine and deep soil. Fineness of 
texture near the surface is of great advantage to many 
plants, although unfavorable to certain kinds of trees. 
The importance of such waste sheets to mankind can 
hardly be overestimated. 

The even surface of the lava plateau of southeastern Wash- 
ington is covered with a heavy sheet of waste, at places 50 
or more feet thick. Deep sections show hard black lava at 
the base, gradually changing upwards to a yellowish decayed 
mass, and becoming a very fine porous soil towards the surface, 
where all traces of rock structure have disappeared. The soil 
offers scarcely more resistance to the plow than so much meal. 
Great wheat crops are raised upon it. 

Local and Transported Soils. — Soils may be roughly 
classified as local and transported. A local soil consists of 
waste still lying upon or near the rock from which it was 
weathered. A transported soil consists of waste that has 
been carried a greater or less distance from the parent 
rock. 

In a region of local soils there may be a great difference 
in the value of neighboring farms, according as they lie on 
rocks that yield rich or ^ or soils. The famous Blue Grass 
district of central Kentucky possesses a fertile soil weathered 
from limestone. Adjoining on the south and east is a belt of 
sandy rocks, where the soil is hardly worth cultivating. The 
contrast in the value of the farms and in the condition of the 
people of the two districts is very striking. The same con- 
trast is to be seen in passing from the rich limestone soils 
around Nashville in western Tennessee to the " barrens " on 
the surrounding sandstones. 

Meadows and valleys generally contain transported soils 
supplied by the waste that is washed down from the adjoining 
hillsides and from the upper part of the valley. 



THE WASTE OF THE LAND. 



269 



Transported soils usually possess a greater variety of com- 
position than local soils, and are therefore more generally 
suitable to varied crops. Further account of them will be 
found under flood plains (p. 279), wind action (p. 316), and 
glacial action (p. 335). 

Rock Ledges and Cliffs. — On surfaces of steep descent, 
such a,s occur along the fault cliffs of blocked plateaus, or 
on the flanks of newly uplifted mountain masses, the waste 
is rapidly moved downward, leaving the bare rock exposed 
on the upper slopes. The steep sides of young valleys, 
cut by vigorous streams in structures of any kind, are also 
usually bare and rocky 
on their upper slopes, 
because the waste is 
there removed as rap- 
idly as it is supplied; 
their lower slopes are 
cloaked with sheets 
and streams of loose 
stone and gravel. 

In contrast to the 
deep and fertile waste 
sheets of plains, the 
steep and bare rock 
ledges of plateaus and 
mountains are "des- 
erts." They are avoided ^'^- "*• ' """^ '""^ ''"^"" 
by nearly all forms of plant and animal life. Lichens and 
mosses may attach themselves here and there ; small plants 
of higher order may gain root-hold in occasional crevices ; 
lowly refugees, brute or human, may seek shelter in shallow 
caverns beneath overhanging ledges ; but a steep and bare 
rock surface is too sterile to attract numerous occupants. 




270 



PHYSICAL GEOGRAPHY. 



Land Slides. — Land slides from rocky cliffs may form 
tumultuous heaps of waste beneath the cliffs, or may 
spread smoothly along the valley floor. A slide may, in 
its excess over the ordinary falls of small rock masses 
from a cliff be compared to a cloud-burst flood in the 
stream channel of an arid region. 




^L.' 


gS"" 








^v^-:-;:^ 


^•iy,-A , ^ 


"■ ■■.):^:4#i'tts^ 


^MMH^^ 


pi-iSvSS^ 


W 


1^ 




Wm 


m 




: : 


" 


W^^^^KK/U^^^^:^^*- '^S^ ^S^^l 




J:>;;ffi^; 








•-: ::1 


M^2^ 



Fig. 176. — Land Slides in the San Juan Mountains, Colorado. 



Certain valleys of the Eocky mountains of southern Colo- 
rado contain numerous slides of great dimensions. It is 
thought that the slides may have been dislodged by earth- 
quakes. Although soon overgrown with trees, they are easily 



THE WASTE OF THE LAND. 271 

recognized by their hummocky form, and by their relation to 
scarred cliffs on the overlying slopes. The slide shown in 
the valley of Fig. 175 measures two and a half miles along 
the mountain base. 

Waste Slopes. — The rocky talus beneath the cliffs, 
peaks, and ledges of high plateaus and lofty mountains 
is a sheet of slowly moving waste. Its angle of descent 
(generally from 30° to 40°, decreasing somewhat toward 
the base) is delicately adjusted so as to strike a balance 
between the supply and the removal of waste. 

The active supply of coarse rock blocks from a high cliff 
requires a steep slope in the talus below, for only on a steep 
slope can the talus blocks be removed as fast as they are sup- 
plied. A slower supply of finer waste allows the production 
of a less steep talus. 

Weathering goes on beneath the creeping talus, and the 
waste thus supplied joins the rest in a slow movement 
down the graded slope. An artificial cut may reveal the 
dragged arrangement of the creeping waste sheet, the faster 
movement of the surface parts being easily recognizable. 

As mountains and plateaus become older, the peaks and 
cliffs are more worn away and the waste sheet covers a 
large part of the surface. It is for this reason that the 
profiles of maturely dissected mountains present so many 
lines of regular descent at a comparatively constant angle. 
Only the strongest rocks still stand out in cliffs ; the less 
resistant rocks are alreadj'^ worn back to smooth slopes, 
almost wholly cloaked with sheets of creeping waste. 

The great painters of several centuries ago sometimes rep- 
resented mountains with fantastic and impossible outlines, in 
which the steepness of the slopes was altogether unnatural. 



272 



PHYSICAL GEOGRAPHY. 



At that time the study of land forms had hardly begun. It is 
still the habit in modern descriptions to exaggerate the steep- 
ness of mountain slopes. In careful descriptions the propor- 




Fig. 176. — The Slope of Pikes Peak. 



tions of bare cliffs and of waste-covered slopes should be 
accurately noted. The flanks of Pikes Peak consist in large 
part of even waste-covered slopes, and illustrate the impor- 
tance of this class of forms. 



The cloak of rock waste on a graded mountain slope 
weakens the attack of the weather on the rocks under- 
neath the waste. The bare peaks and ledges that stand 
out above the slant of the waste slope are unprotected, 
and in spite of their resistant structure, they crumble away 
with relative rapidity, until they are worn down to a slope 
on which the waste sheet will lie. Hence in lofty moun- 
tains the sharper peaks must be regarded as comparatively 
short-lived forms. 



THE WASTE OF THE LAND. 273 

In certain mountain ranges many peaks have an almost 
equal altitude, differing only by a small part of their total 
height. To an observer standing on one summit many others 
seem to rise to about the same level, like wave-crests at sea. 
It has been suggested that the approach to even height results 
from the rapid weathering and destruction of the bare peaks 
that rise to unusual heights above the slant line of the waste 
slopes on the valley sides. The Rocky mountains and the 
Alps present many cases of this kind. The slopes of the 
dissected block mountains of Utah (Fig. 103) are generally 
smoothly covered with waste, above which bare peaks seldom 
rise to great height. 

If for any reason the process of removal gain the advan- 
tage on a waste-covered mountain side, the waste sheet 
will be stripped away, exposing a bare rocky surface of 
even slope. The weather will then actively attack the 
uncovereii rock ; the weaker parts will be first hacked out, 
changing the even slope to a ragged profile. In time a 
new even slope will be established, and the surface will 
be again covered with waste. 

The. chief causes that lead to a stripping of a waste- 
covered slope are : an uplift of the region and a revival 
of the valley streams, whereby the valley is deepened and 
the waste on the side slopes is quickly removed ; a tilt- 
ing of the region, whereby certain slopes are made steeper 
than before, and the forces of removal on them are 
strengthened ; a change of climate, whereby the forest 
cover is destroyed and the processes of washing and creep- 
ing are allowed to remove much waste that was before 
detained by tree roots. 

When forests are extensively cut from waste-covered moun- 
tain sides, a large part of the waste may be washed off, 



274 PHYSICAL GEOGRAPHY. 

leaving great slopes of bare rock or of coarse stony waste. 
Uncliecked torrents then cut gulches in the slopes and deso- 
late the valley floors with the gravel and sand washed down 
vipon them. Great injury has been done in this way in the 
Alps and the Pyrenees. On some deforested mountain flanks 
terraces have been built and trees planted to detain the waste 
upon the slopes and to re-forest them. 

It is probable that the successive processes of waste- 
covering, stripping, and covering again may occur as many 
times as vigorous mountains are disturbed by uplift or tilting. 
When disturbances become less frequent, graded slopes may 
be more continually developed ; then the more vigorous forms 
are subdued and the old age of the mountains comes on. 

As the old age of a land form is approached, bare ledges 
decrease in size and number, rock waste is supplied less 
rapidly, the waste-covered slopes are reduced to gentler 
declivity, and the movement of waste upon them is 
slower and slower. With longer exposure to the .weather 
the surface waste becomes less stony ; and with slower 
removal the waste cloak becomes thicker. Thus, as relief 
decreases, a larger and larger part of the surface acquires 
a soil suitable for cultivation; 

There is a dissected upland of nearly horizontal strata 
forming a district of gently rolling hills (an upland enclos- 
ing an inner lowland) in southern Wisconsin, where the whole 
surface is smoothly graded over with soil. . Hardly a ledge 
is anywhere to be seen. The activity of the processes by 
which the waste is supplied is everywhere equal to the activ- 
ity of the processes by which it is urged to move down the 
slopes. Along every downhill line the streams of waste are 
creeping leisurely towards the valleys. But so slowly does 
even the finer surface waste move that the district is clothed 
with an abundant prairie vegetation, or yields a rich farm 
harvest. 



THE WASTE OF THE LAND. 275 

The Piedmont district of Virginia and the Carolinas, an old 
worn-down mountain region, has a thick waste sheet with fine 
surface soil on its flat interstream uplands. Deep cuts dis- 
close a gradual change from firm rock, 20 to 50 feet under- 
ground, to fine soil above, where only the least destructible 
minerals (like quartz) remain in stony or gritty fragments. 

The presence of vegetation is an important factor in 
determining a balance between the process of waste supply 
and removal. Hence even on surfaces of moderate relief 
a change from grass or forest to plowed field calls for 
constant vigilance on the part of the farmer, lest his 
surface .soil be washed away. "Contour plowing" (fur- 
rows running around the slopes in level lines) is then 
recommended, so as to detain the surface wash. 

If a small gully is cut in a hillside field by the run-off 
of a heavy rain, it should be clogged with stone and brush 
before it grows to ungovernable size. This matter is so 
important that an illustrated chart in explanation of it has 
been prepared for distribution by the U. S. Department of 
Agriculture, Washington, D. C. 

The Forms Assumed by Stream-Swept Waste. 

Alluvial Fans of Torrents. — The waste that creeps and 
washes down the sides of a valley is delivered to the 
stream that follows the valley floor. The form then 
taken by the waste depends largely on the behavior of the 
stream. A torrent receiving much coarse waste from a 
steep-sided ravine frequently sweeps so much of it into the 
main valley that it cannot all be carried away by the master 
river. The coarser part of the waste then accumulates in 



276 



PHYSICAL GEOGRAPHY. 



a cone-like form, known as an alluvial fan, spreading with 
even slope from the ravine mouth into the main valley. 

Alluvial fans have a steep slope when formed by small 
torrents bearing a coarse and plentiful load. They have a 
flat slope when formed by large streams with a fine-textured 
load. They are small or wanting in very young valleys ; they 

may grow to great size 







in maturely developed 
valleys. 

As a young ravine 
is gnawed into a lofty 
slope, the fan at its 
mouth may grow ac- 
tively forward into the 
main valley. The fan 
then drives the master 
river against the fur- 
ther side of the valley, 
where it under-cuts 
the valley wall. The 
fan still growing, the 
river may be ob- 
structed and thus re- 
quired to spread over 
the valley floor up 
stream from the fan, 
forming a shallow 
lake, while on the 
down-stream side the 
river descends in rapids over the coarsest boulders brought 
down by the torrent. 

The growth of fans is well illustrated by those formed by 
torrents entering the east end of Lake Geneva, Switzerland, 
where excavations have discovered ruins of Eoman settle- 
ments at a depth of 5 feet, and of the prehistoric "stone 




Fig. 177. —Alluvial Fans. 



THE WASTE OF THE LAND. 277 

age " at a depth of from 15 to 20 feet. Here fan building 
has gone on at a rate of about 3 feet in 1000 years. 

The channel of a torrent on its fan is enclosed by low 
walls of coarse waste that is strewn on each side at time 
of flood. The torrent is thus naturally diked. When a 
great quantity of waste is brought from the upper slopes, 
the channel may be choked near the head of the fan. The 
torrent then switches off on a new course and enters the 
main river at a new point on the margin of the fan. 

Two-Ocean creek, a small stream in the Yellowstone park, 
has built a fan that forms a part of the continental divide. 
Sometimes the stream flows on an eastern radius that leads it 
to Atlantic creek (Missouri-Mississippi system), sometimes on 
a western radius, to Pacific creek (Columbia system). 

In the Alps, villages are built and fields are cultivated on 
the fans of large size. When the torrent of such a fan is 
turned on a new course, it may flood fields and villages, caus- 
ing much damage. A valley road traversing the fan is swept 
away where the torrent then crosses it, while the bridge over 
the former torrent channel is made useless. 

Accidents of this sort are common in mountain regions. 
In 1896 a stream entering a lake in Switzerland overflowed 
its fan with a stony flood fed by a landslip in the head 
ravine. It laid waste a strip 2 miles long and over 300 
feet wide at the forward end, covering it with a layer of 
stony mud 10 or 12 feet thick. The advance of this curious 
flood was sometimes so slow that the grass on the fields in 
front of it was saved by hasty mowing. Houses were pushed 
out of place, a road and a railroad were buried. Por a time all 
travel had to go by boat on the lake. The people who lived 
on the fan had some compensation for their losses in carry- 
ing the thousands of visitors to and from the scene of the 
disaster. 



278 



PHYSICAL GEOGRAPHY. 



A torrent usually gives mucli ground water to the 
loose-textured fan, and therefore decreases in volume on 
passing out of its rock-walled ravine. The ground water 
commonly reappears in springs near the base of the fan, 
and the spring line is often marked by a peculiar vegetation. 

Filled and Terraced Valleys. — When a young stream 
has graded its channel, it begins to broaden its valley 
floor and form a flood '■M^\\1\P"'\ 



plain by swinging 
from side to side, as 
has already been ex- 
plained. It may then 
happen that the head- 
waters and upper 
branches, still gnaw- 
ing into the uplands 
and dissecting them 
more and more thor- 
oughly, bring a larger 
load of waste down their numerous gulches and ravines 
than the main stream can sweep down the moderate slope 
that it has adopted. Some of the increasing load is then 
laid down on the flood plain, steepening its slope, and 
thus hurrying the river to a velocity that enables it to 
carry the rest of the load. The flood plain thus grows 
higher and builds up on the valley sides. A similar effect 
is produced when the slope of the trunk river is lessened 
by a warping or tilting of the region. 

Fig. 178 illustrates a valley in steep mountains, cut down 
by a strong river. By increase of load from the headwaters, 




Fig. 178. —An Eroded Valley. 



THE WASTE OF THE LAND. 



279 



the river comes to be unable to carry along all the waste that 
it receives. The valley is thus filled with a growing flood 
plain, as in Fig. 179. The waste is here chiefly supplied 
by the headwaters, 
while in Fig. 177 it 
comes chiefly from the 
side streams. 

The lower course of 
the Missouri river 
seems to flow on a grow- 
ing flood plain, for its 
alluvial deposits are 
much deeper than its 
channel; here the waste 
is chiefly supplied from 
the upper waters of the 
main river. 




Fig. 179.— A FiUed Valley. 



Flood plains of gentle slope contain a deep layer of 
fine rock waste, an excellent soil for plants. The deep 
waste contains a large quantity of ground water. At 
every flood a new layer- of waste is added to the surface, 
and the finest particles sink with the water into the 
ground. Thus the soil is naturally renewed, and its 
fertility is long enduring. 



The Eed river of Louisiana offers a remarkable illustration 
of a growing flood plain. Its headwaters, gnawing into the 
Llano Estacado of Texas, gather a greater amount of waste 
than can be carried down the gently sloping valley that the 
trunk river has . developed in Louisiana. The trunk river is 
therefore slowly building up its flood plain. The building of 
the flood plain is aided by the growth of the famous " Eed 
river raft," an accumulation of many fallen tree trunks that 
obstructs the river channel for a number of miles, dividing 



280 



PHYSICAL GEOGRAPHY. 



the current into many small channels, checking its flow, and 
causing the waste brought from the upper valley to settle. 

So rapidly does the Red river build up its flood plain that 
its side streams cannot build up the plains in their valleys 

at equal rate ; lakes, 
therefore, gather in 
the side valleys, like a 
series of leaves along 
the Red river stem. 

After filling its 
valley with waste for 
a time, a river may 
change its action and 
entrench its course 
in the built-up flood 
plain. The part of 
the plain then re- 
maining above the 
new valley floor is 
commonly called an 
alluvial terrace, or 
simply a terrace (Fig. 
181). The change 
in the action of the 
stream may be either 
because the supply 
of waste from the headwaters decreases, or because the 
lower course of the valley is deepened, or because the slope 
of the stream is increased by a warping of the region. 

Terraces often afford excellent sites for villages, out of 
reach of floods ; but they are generally less fertile than the 
flood plains, for want of suflicient ground water. 




Fig. 180. — Flood Plain of Red River, Louisiana. 



THE WASTE OF THE LAND. 



281 



Some of the inner valleys of the Himalaya, up stream 
from deep gorges, have been heavily filled with waste, pro- 
ducing plains several miles broad among the mountains. But 
the warping that caused the filling seems to have weakened 
or ceased long ago, for 
the rivers have now 
cut their outlet gorges 
so deep that the former 
flood plains are deeply 
trenched, in some 
places exposing their 
layers of sand and 
gravel to a depth of 
3000 feet, and thus 
forming gigantic ter- 
races. 

Fig. 181.— A Terraced Valley. 

Waste-Filled Basins. — Where rivers have worked long 
enough, they destroy the lakes of their youth, partly by 
depositing sediment in the basins, partly by cutting down 





the outlet ; that is, by filling and draining the lake basin. 
The lake is then replaced by a plain watered by inflowing 
streams from the head and side slopes, and drained by a 
river which escapes through a narrow outlet valley, often 
rock-walled and- gorge-like. 

Lake Erie has a smooth floor covered with fine sediment. 
When the lake waters are withdrawn by the sufficient lowering 



282 



PHYSICAL GEOGRAPHY. 



of their outlet, the lake floor will be revealed as a smooth 
plain. 

The best agricultural land in the neighborhood of Mount 
Shasta, Cal., is found in the flat-bottomed basins, or '< meadows," 
which represent the waste-covered floors of lakes that were 




Fig. 183. — A Warped VaUey. 

formed by lava-flow barriers from the neighboring volcano. 
The discharge of some of the lakes is so recent that their 
meadows are still too swampy for occupation. 

The effect of warping movements of the earth's crust in 
making streams lill up one part of their valley and wear 

down another has 
already been men- 
tioned. Filled val- 
leys and trenched 
gorges of this 
origin are charac- 
teristic of lofty 
ranges where 
mountain growth 
is still in progress. 
The gorges are 
often so steep as 
to be impassable ; but the filled depressions are important 
because they offer dwelling places to mountain peoples. 

The upper Arkansas valley, back of the Front Eange of the 
Eocky mountains, is a warped basin, floored by plains of waste 




Fig. 184. — A Waste-Filled Basin, Southern California. 



THE WASTE OF THE LAND. 



28J 



that slope forward from the mountain sides. The river has 
cut through the enclosing range in a deep canyon, called the 
Royal Gorge, now followed by a railroad. In the future the 
deepening of the canyon (where the river is now actively 
wearing down the rocky bed) may permit the upper river to 
dissect the basin plains ; but at present such dissection is 
only just begun, dividing the valley into low bench-land and 
flat flood plains. 




Fig. 185. — A Plain of Mountain Waste, SontheaBtern California. 

At first sight a warped and filled valley of this kind 
would he taken to mark the place of an extinct lake ; but 
it is very probable that in many cases the warping of the 
valley was so slow that no lake was produced, the depres- 
sion being filled and the uplift being cut down as fast as 
the warping proceeded. 

The waste from the mountains is here detained for a time 
in its journey to the sea, and in this respect the waste of a 



284 



PHYSICAL GEOGRAPHY. 



filled basin resembles the water of a lake. But just as the 
lake is short-lived compared to the mountains, so the waste- 
filled basin is only a temporary feature. As the outlet valley 
is deepened, the journey of the waste toward the sea will be 
resumed, and in due time it will reach its goal. 







i^l^^jz^t^j'? 



; >?*_>*-',^^:^ '^'is.ss^^-^'^M^- -%" 







Fig. 186. — A Meandering River, Vale of Kashmir. 

The Vale of Kashmir, enclosed by the outer ranges of 
the Himalaya in northwest India, is a famous example of 
this kind. It is a waste plain in a broad basin, of area 
about equal to that of Connecticut, occupying a down- 
warped district between lofty mountains. Many streams 
gather from the mountains and unite to form the Jhelam 
river, which meanders across the plain (Fig. 186) and 
escapes from the west end of the vale by a deep gorge 
through the enclosing range. 

The outlet gorge has been cut a little below the general 
level of the plain, allowing the streams to entrench their 
courses to a moderate depth, and thus forming many fertile 



THE WASTE OF THE LAND. 



285 



flood plains. A shallow lake (Wular) lies near the outlet, as 
if not yet filled, or as if lately produced by renewed warping. 
Until recent years the only access to this beautiful vale 
was by a high pass over the outer range ; but now a road 
leading through the gorge has been made by British engi- 
neers. Although difficult to construct and to maintain, it has 
greatly facilitated traffic 




and trade between the vale 
and the outer plains. 

The oval plain of Hun- 
gary, about 200 miles in 
diameter, is a fine example 
of a filled basin enclosed 
by mountains. The inflow- 
ing rivers have cut down 
their flood plains a little 
below the level of the grav- 
elly marginal slopes ; but 
they wander freely over the 
central plain of fine silts 
(Fig. 154). The outlet, 
where the Danube has cut 
the gorge of the Iron Gate 
through the Transylvanian 
Alps, has long been ob- 
structed by rocky rapids, 
recently blasted away to improve navigation. Although the 
plain has many resemblances to the floor of a former lake 
basin, the deposits on its surface all appear to have been 
formed by river action. 

Green river basin in southwestern Wyoming is an exten- 
sive depression measuring over 100 miles in diameter. Its 
heavy deposits of waste, once washed in from the surround- 
ing mountains, are now deeply dissected ; for the outflowing 
Green river has cut a deep canyon through the enclosing 
Uinta mountains on the south. The formerly even floor of the 



Fig. 187. — The Green River Basin, Wyoming. 



286 PHYSICAL GEOGRAPHY 

waste-filled basin has been converted into a dissected upland, 
with valleys sometimes 1000 feet deep. Much of the long- 
detained waste has gone forward again on its way to the sea. 
Being dry as well as rugged, the basin is of little value for 
settlement, except where beds of coal attract mining or where 
irrigation is possible in the valleys. 

Flood Plains of Large Rivers. — The flood plain of a 
large river is formed at such a slope that its gain and loss 
of waste are about equal. Loss is caused chiefly by cut- 
ting away the outer bank of the curving channel, where 
the current runs fastest. Gain is caused by adding waste 
on the inner bank of the curves, where the current is 
slowest ; and also at time of flood when the river deposits 
much waste on the plam near the banks of the channel, 
where the first loss of velocity in overflow greatly decreases 
its carrying power. The flood plain is in this way built 
up chiefly near the river, and its surface therefore has a 
faint slope to the right and left of the channel banks. 

On the Mississippi flood plain the slope away from the 
river is 5 or 10 feet to a mile. This is much greater than 
the slope down the flood plain, which is about half a foot to 
a mile. 

As a consequence of the gentle slope of a flood plain 
away from the river banks, the sides of the plain are 
poorly drained and are often occupied by back swamps. 
Villages on broad flood plains are frequently located close 
to the river bank, where the plain is highest. 

A large river seldom receives small tributaries while flow- 
ing through its flood plain ; for small streams cannot enter 
it against the side slope of the plain. Indeed, many small 



THE WASTE OF THE LAND. 



287 



streams may rise on the plain and run obliquely away from 
the main river, joining streams from the uplands, and fol- 
lowing the lowest available channel 
through the back swamps. 

A remarkable example of this kind 
is seen on the Mississippi flood plain, 
where the trunk of the Yazoo river 
system, gathering little branches from 
the uplands on the east and from the 
fiood-plain slope on the west, flows 
about 180 miles through the back- 
swamp district, unable to enter the 
main river. The Yazoo might pursue 
an independent course all the way to 
the gulf, if the Mississippi did not 
happen at present to swing across to 
the bluffs at the eastern side of the 
flood plain (where Vicksburg is located 
in order to be near the river), and 
there take in the Yazoo. 

The waste on a flood plain rests 
for long periods after it is deposited 
at times of river overfloM^. When 
the plain is cut away as the river 
channel shifts, the waste moves a 
less or greater distance forward to 
another resting place, wearing and weathering finer and 
finer as it travels slowly down the valley. 




Fig. 188. — The Mississippi 
Flood Plain. 



The flood plain of the middle Rhine in western Germany 
is a fertile belt of land, occupied by a large agricultural popu- 
lation, between forested uplands on the east and west. The 
river has been " corrected," that is, turned from its meander- 
ing course into a nearly straight channel ; its banks are 



288 PHYSICAL GEOGRAPHY. 

diked so as to prevent overflow. It is possible that another 
century may see the vast flood plain of the Mississippi thus 
made much more available for occupation than it now is. 

Stony flood plains may be formed in relatively steep valleys,, 
if they are actively supplied with coarse waste from their head 
and side slopes. Although washed by streams of rapid current 
and torrential behavior, such flood plains belong in the same 
class of forms with the fine-textured flood plains of large 
rivers. The slope of the plains and the texture of their 
materials are unlike ; but the fact that both are flood plains 
formed by their streams gives them a close relationship. 

Alluvial Fans of Large Rivers. — When large rivers 
flow from mountains or plateaus to open lowlands, where 
no valley walls enclose them, they may build extensive 
alluvial fans of faint slope. The Merced river of Cali- 
fornia (see M, Fig. 190) offers a good illustration of this 
habit. 

The Merced gathers much waste from its steep headwaters 
in the Sierra Nevada. On issuing from its narrow valley at 
the mountain base, it is free to turn to the right or to the left 
on the broad " valley of California," a low trough between 
the Sierra and the Coast range. Here the river has built a 
fan of about 40 miles radius, of gravel near the mountains, of 
fine silt farther forward. 

The rain of this region falling chiefly in winter, it is nec- 
essary to irrigate the fields for summer crops. Nothing could 
be better adapted to the needs of irrigation than a gently 
sloping alluvial fan ; for the river may be easily turned into 
various channels at the head of the fan and led forward on 
different courses, and thus distributed over thousands of 
acres. The fan of the Merced was a cattle range under Span- 
ish occupation in the first half of the nineteenth century ; it 
became a wheat region in later years ; and since irrigating 



THE WASTE OF THE LAND. 289 

canals have been constructed, it has been largely planted with 
fruit orchards. 

One of the largest alluvial fans in the world is that of 
the Hoanglio, in eastern China. This great river, bear- 
ing a heavy load of fine silt from the basins among the 
inner mountains, issues from its enclosed valley 300 miles 
inland from the present shore line, and at a height of 
about 400 feet above sea level, and then flows to the sea 
down the gentle slope of its extensive fan. 

The great fan of the Hoangho is very fertile, and sup- 
ports one of the densest populations of the earth ; but it is 
subject to overflow on a vast scale, when the river suddenly 
changes its course from one path to another, and invades 
fields and villages on a new course to the sea. Overflow 
is restrained as far as possible by dikes ; but the channel has 
repeatedly been changed during the many centuries of Chi- 
nese history. The mouth of the river has thus been shifted 
more than 200 miles north or south. The hilly district of 
Shantung, once an island, has been converted into a peninsula 
by the forward growth of the great fan. 

" The destruction caused by these overflows is awful beyond 
description ; the loss of life is very great, and the destruction 
of crops that form the means of support of millions produces 
famine and the overrunning by starving hordes of the more 
fortunate districts of the adjacent country. The anarchy 
that rules in this struggle for life is almost beyond the con- 
ception of those who inhabit lands where the population is 
much below the capacity of the country, or which are easily 
reached by foreign supplies." 

During wars " the river has been turned to account as a 
weapon of offence. Breaking the embankments has been 
made to accomplish, almost instantaneously, by the destruc- 
tion of hundreds of thousands of inhabitants, conquests that 



290 



PHYSICAL GEOGRAPHY. 



had been delayed by years of brave resistance." The flood 
of 1887 covered an area estimated at 50,000 square miles, 
immensely fertile and swarming with villages. The num- 
ber of people drowned was at least a million, and a greater 
loss followed from famine and disease caused by the flood. 

River-Made Plains. — When many rivers flow forth 
from mountain valleys upon a neighboring lowland, their 
adjoining fans unite in a broad plain sloping gently for- 







rig. 189. —View on River-Made Plain of Northern India. 

ward from the mountain base.- This may be called a river- 
made plain, in distinction from coastal plains, lava plains, 
and worn-down mountain lowlands. A river-made plain 
often occupies the depression between two highlands or 
mountain ranges, as between the Himalaya and the 
plateau of southern India ; it will then slope from each 
side toward a midway depression. The streams from the 
various fans will be gathered by a trunk river meandering 
along the depression. 



THE WASTE OF THE LAND. 



291 



The many rivers issuing from the valleys of the Sierra 
Nevada and the Coast range upon the " valley of California " 
have formed an extensive plain, of which the Merced fan, 
described above, is only a part. The successive fans are so 
broad and fiat that their slightly convex form can' hardly be 
recognized without the aid of surveying instruments. Nearly 
all the streams run in shallow 
channels but little beneath the 
gently sloping surface of the fans. 
The fans from the east and west 
meet in a broad flat-floored trough. 

The trunk river in the depres- 
sion of a two-sided river-made 
plain is pushed away from the 
base of the higher mountains by 
the stronger forward growth of 
their fans. The fan of a large 
stream may form a low barrier 
across the path of the trunk river 
and enclose a shallow lake. 

The San Joaquin river, gather- 
ing streams from the Sierra jSTevada 
and Coast range in the southern 
part of the " valley of California," 
lies nearer to the lower mountains. 
The upper streams of the " valley " 
have been ponded back by the fan of King river (K, Fig. 190), 
forming Tulare lake, a shallow water sheet with indefinite 
marshy shores much overgrown with reeds (Spanish, tules). 

Extensive river-made plains built upon Piedmont low- 
lands are the natural accompaniment of deep valleys ex- 
cavated in the lofty mountain background. The waste 




Fig. 190. — The VaUey of California. 



292 PHYSICAL GEOGRAPHY. 

taken from the latter has supplied the material for the 
growth of the former. The two are found together in 
many parts of the world. 

Extensive river-made plains have been formed both north 
and south of the Alps. On the south, the Po runs between 
the long plain built forward from the valleys of the high 
Alps and the shorter plain built from the valleys of the 
lower Apennines. Many of the streams here are some- 
what entrenched beneath the general level, having begun to 
cut valleys in the plain they had previously built up. Near 
the Alps the material of the plain is coarse ; rain and streams 
sink into the ground, and the surface is relatively dry and 
infertile. Further forward the ground water issues in numer- 
ous springs, and the rest of the surface is very fertile and 
densely populated. The " spring line " separates these two 
parts. 

jSTorth of the Alps the branches of the Ehine and the Dan- 
ube are entrenched in an uplifted river-made plain that was 
built when the region stood at a less elevation. Some of the 
valleys are 1000 feet deep, and the former plain is here 
reduced to a series of ridges extending forward between 
neighboring valleys. 

Deltas. — When a river enters a lake or the sea, its 
current is checked. The finest part of the waste may 
be swept away by waves and tides ; the rest accumulates 
at the river mouth and builds up a new land surface, 
called a delta, in advance of the original shore line. 
Small deltas are characteristic of young rivers ; the longer 
the progress of river growth without interruption by 
uplift or depression, the larger the delta may become. 

When rivers bearing fine waste enter the sea, the settling 
of the waste is favored not only by loss of velocity, but also 



THE WASTE OF THE LAND. 



293 



NORTB PASS 



by the presence of salt in the sea water, which causes sus- 
pended sediments to settle faster than they would in fresh 
water. 

The land surface of a delta is built on the same slope 
as that of the river flood plain further up stream, the delta 
being only the forward part of the flood plain. 

The great fan of the Hoangho may be regarded as its 
delta, because it has been built forward into the Yellow sea 
(so named from the color given by the river waste) ; but it 
cannot be said that the 
whole area of the fan 
was once occupied by 
the sea ; part of it 
may have been built 
on land. 

A river frequently 
splits into several 
channels on the con- 
vex surface of its 
delta ; the outgoing 
branches being known 
as dist7-ibt(taries. 
These are well exhib- 
ited in the finger-like 
division of the Mississippi on its outer delta (Fig. 191), and 
in the many channels of the Ganges and the Brahmaputra on 
their compound delta at the head of the Bay of Bengal. 

The deltas of large rivers consist of fine-textured waste 
or silt, worn during the long journey from the river head- 
waters, and weathered during many rests in the flood plain 
on the way. In a favorable climate deltas are very fertile 
and attract a large population. The three densest popu- 




QRAND PASS 
=^ a SOUTHWEST PASS 



JETTIES 
SOUTH PASS 



Fig. 191. — The Delta of the MisBissippi. 



294 PHYSICAL GEOGRAPHY. 

lations of the world (outside of large cities) are in eastern 
China, northeastern India, and northern Italy ; all on the 
lower flood plains and deltas of large rivers. 

Although attractive on account of fertility, deltas are sub- 
ject to dangerous overflows from land and sea. Kiver floods 
spread over them, unless kept off by extensive dikes such as 
have been built on the above-named deltas. 

Sea floods on deltas are also destructive. When low 
atmospheric pressure and on-shore hurricane winds happen 
to occur with a strong high tide, the sea water may rise over 
the shore dikes and overflow great tracts of delta plain. 
One hundred thousand people were drowned on the delta 
plain of the Ganges and Brahmaputra, India, by a sea flood 
during a severe storm in 1876. 

The deltas or fans of torrents descending directly from 
mountains into the sea are of coarse stony texture, relatively 
unattractive to settlement. Many torrent deltas, the forward 
part of stony fans, are formed at the base of mountains on the 
coast of Japan. 

The rate of growth of deltas depends on the ratio 
between the volume of waste brought by the river and 
the activity of the waves and currents on the shore. 
Great rivers may build their deltas in the face of waves 
and tides. The building of deltas by smaller rivers is 
favored by protection from waves in bay heads and by 
weaker tides. 

The deltas of various large rivers are built in seas having 
distinct or strong tides. At the Mackenzie delta the tidal 
range is 3 feet ; at the ISTiger, 4 feet ; at the Hoangho, 8 feet ; 
at the Ganges-Brahmaputra, 16 feet. 



THE WASTE OF THE LAND. 



295 



The forward growth of deltas often partly fills the 
embayments of half-drowned mountains, as may be seen 
in many of the fiords of British Columbia. The delta 
plain of Fraser river is a fine example of this kind. 
Outlying islands are sometimes tied to the mainland by 
the forward growth of deltas. Several examples of this 
kmd are known in the Mediterranean. 



Elvers of comparatively small size build deltas in the pro- 
tected bays of (nearly) tideless seas. Deltas are therefore 
common in the bay 
heads of Greece ; 
here the partial sub- 
mergence of a moun- 
tainous country has 
produced a ragged 
shore line in a sea 
where the tidal range 
is small ; ma^ny of 
the bay heads have 
been much short- 
ened by delta growth. 
The sloping delta 
plains contain a 
large part of the 
coastal population. 

Small streams 
may be strong 
enough to build 
deltas in lakes. In Lake Geneva, Switzerland, many torrents 
have built sloping fan deltas in the quiet waters. The fans 
are generally occupied by villages. When large buildings are 
erected close to the water's edge, the delta margin is over- 
weighted, and it may slip into the lake. Numerous accidents 
of this kind have occurred. 




Fig. 192. — Torrent Fan, Lake Geneva. 



296 PHYSICAL GEOGRAPHY. 

The absence of deltas at the mouths of certain rivers is 
frequently not so much on account of the action of tides 
in sweeping away the river silt, as because there has not 
been time enough to build a delta since the present posi- 
tion of the land was taken. 

The lower valleys of the Delaware, Susquehanna, Potomac, 
and neighboring rivers are drowned, forming bays in the 
partly submerged coastal plain of the middle Atlantic states. 
Whatever deltas these rivers previously built are now beneath 
the sea. Soundings in the lower Delaware bay have, it is 
believed, discovered a drowned delta traversed by the chan- 
nels of several distributaries. Very little delta growth has 
yet taken place at the bay heads ; hence it must be concluded 
that the depression of the region is recent ; it may still be in 
slow progress. 

Very large rivers may build forward their deltas in spite 
of a slow depression of the coastal region. Thus the delta of 
the Mississippi has actively advanced into the gulf waters ; 
while Galveston bay on the west and Mobile bay on the east 
indicate a moderate depression of the region, which the rela- 
tively small rivers entering those bays (formerly valleys) 
could not wholly counteract by delta building. 

Dissected Deltas. — When a region is broadly uplifted, 
as in the formation of a coastal plain, the deltas of the 
former shore line will be dissected by the rivers that built 
them. Such deltas are seldom conspicuous forms, unless 
built of coarse waste with a steep front slope. 

During the submergence in which the topmost layers of 
the Atlantic coastal plain were deposited, the Delaware built 
a gravelly delta at Trenton, IST. J. Since uplift, the river has 
trenched the delta, forming terraces on each side of its new 
valley. It is probable that many similar dissected deltas 
occur along the inner margin of the Atlantic coastal plain. 



CHAPTER XL 
CLIMATIC CONTROL OF LAND FORMS. 

The Several Classes of Climatic Controls. 

Direct Climatic Controls. — An earlier chapter contains 
a brief description of tlie several zones into wliich the 
earth's surface may be divided on account of the unequal 
action of sunshine on its globular surface. The average 
atmospheric temperatures prevailing in the different zones 
are certainly among the most important geographical con- 
trols that are exerted upon man's ways of living. The 
distribution of rainfall has also been shown to be an 
important agent in determining whether a region may be 
fertile or barren, populous or deserted. Climatic controls 
of this class, depending on the physical condition of the 
atmosphere as to temperature, moisture, and movement, 
act directly on plants, animals, and man, and greatly 
influence their distribution. 

Indirect Climatic Controls. — All the controls exerted 
on man's ways of living by the various forms of dissected 
land surfaces are, in a certain sense, indirect climatic con- 
trols, for they result from the action of weathering and 
washing, and these processes are in turn controlled by 
climatic conditions. The examples of land forms thus far 
given have been mostly taken from regions of ordinary 
climate, neither very dry nor very cold, and with rainfall 



298 PHYSICAL GEOGRAPHY. 

sufficient to fill all basins to overflowing. A number of 
examples now follow in which the peculiar effects of dry 
and of cold climates are described. It will be shown that 
the forms of the land and the condition of its surface vary 
greatlj'" according to their origin under an ordinary, a dry, 
or a cold climate. 

Changes of Climate. — One of the most remarkable 
results of this division of geographical study is the discov- 
ery that certain existing land forms have been produced 
under climatic conditions quite unlike those prevailing 
to-day. There are regions, now dry and barren, where 
the marks of a former moist climate are very apparent. 
There are others, now 'fertile and populous, where the 
marks of a former cold climate are no less distinct. Not 
until these curious changes in climate are recognized can 
the great variety of land forms and the controls that they 
exert on the earth's inhabitants be clearly understood. 

Effect of Dry Climate on Streams and Rivers. 

Ledges and Waste Slopes. — Certain parts of the world 
have so little rainfall that vegetation is nearly wanting. 
Here rock waste washes and creeps freely down the slopes, 
not being detained by vegetation long enough to be 
weathered to fine texture. Narrow valleys among arid 
uplands are therefore encumbered with stones and gravel. 
The small streams must maintain a strong slope in order 
to carry forward their heavy load. 

As a consequence, the dissected uplands of arid regions 
possess a large proportion of bare rock ledges, such as have 
been described in the plateaus of Arizona. Their rugged 



CLIMATIC CONTROL OF LAND FORMS. 299 

forms must be worn to more gentle slopes before they are 
covered with waste. 

The desolate gray forms of desert mountains, like the 
ranges of northwest Mexico (Sonora) and of northern Chile 
(Atacama), are much less picturesque than the snowy summits 
and forested flanks of mountains in a moister climate. 

Streams of Dry Climates. — When a light rain occurs in 
a region of dry climate, much of the water returns to the 
atmosphere by evaporation, a large part of the remainder 
sinks into the thirsty soil, and the run-off by streams 
is small. Much of the ground water evaporates under- 
ground and passes from the soil as water vapor, instead 
of coming out in springs. When a heavy rain occurs, the 
streams are flooded ; but the water soon runs away, leav- 
ing the channels dry again. 

The streams of dry regions are, therefore, very variable 
in volume ; active for a while after a rain, almost or quite 
disappearing in the long dry seasons, advancing far down 
their, lower courses when in flood, then dwindling and 
withering away and leaving their lower channels dry. 

In the Sahara dry water courses, known as wadies, are 
commonly used for roads, as their defiles frequently offer 
graded ways through rocky uplands. Death by drowning 
would nowhere be so little expected as in a desert ; but it 
sometimes happens that a caravan, following a wady through 
an upland, meets a down-rushing flood fed by rainfall in the 
distance ; and before the travellers can climb the steep walls 
of the defile they may be overwhelmed and drowned. 

In parts of the Kocky mountain region, of generally dry 
climate, heavy rains occasionally fall in summer. Then for a 
few hours the dry channels are flooded with a rushing turbid 
stream, that sweeps away the waste that had been washed in 



300 



PHYSICAL GEOGRAPHY. 



by lighter rains. Camping parties, pitching their tents too 
near a channel that was nearly dry in the afternoon, may be 
overwhelmed by a rushing flood at night. Fig. 193 illustrates 




Fig. 193. — Flood in Cherry Creek, Denver, Colorado. 

a sudden flood in Cherry creek, where it passes through the 
city of Denver, Col. The channel of the creek was dry half 
an hour before this raging torrent rose. 

Streams that are supplied by springs in uplands and 
mountains frequently diminish in volume, partly by evapo- 
ration, partly by sinking into the ground, as they advance 
over arid lowlands. They may wither away and disappear 
entirely from the surface ; but their flow is usually con- 
tinued as ground water for some distance beyond their 
visible end. Their load of waste is spread on the surface 
before them ; hence the lower parts of many streams in 
arid regions build up the surface they flow upon, even 
though high above baselevel. 



CLIMATIC CONTROL OF LAND FORMS. 301 

Certain rivers of Argentina liave not volume enough to 
carry them across the pampas to the sea. Rising in the 
mountains, tliey entrench their valleys 100 feet or more 
beneath the surface of the pampas for some distance, and 
here are the chief settlements, such as the city of Cordoba 
on the Primero ; then, dwindling' in volume, they flow out 
upon the pampas, ending in marshes. 

Flood Plains in Deserts. — Rivers that rise in w^ell- 
watered regions sometimes flow across deserts on their way 
to the sea without receiving branches for long distances, 
and decreasing by evaporation as they advance. If the 
rivers have developed open and accessible valleys, nearly 
all the population of the region is gathered on their flood 
plains. 

The most famous river of this kind is the Nile, which flows 
1000 miles without receiving a branch, except a few small 
wet-weather streams. Its flood plain, entrenched beneath the 
desert uplands, is about 500 miles long and from 5 to 15 miles 
wide, broadening on the delta to over 100 miles. Here most 
of the millions of Egyptians dwell. Their resources are 
almost wholly agricultural, and as such depend on the annual 
inundation of the Nile, caused by the northward movement 
of the belt of equatorial rains in summer. The river flood 
begins in June, usually rising 25 feet or more at Cairo in late 
summer or early autumn. For thousands of years the fer- 
tility of the flood plain has been maintained by the annual 
additions of river silt, estimated to amount to 4i- inches a 
century. 

The southward course of the lower Colorado has few 
branches for about 300 miles. Its water supply comes chiefly 
from the mountains and high plateaus in its upper basin. 
The sediments swept from its canyons have built a delta 
across the depression that holds the Gulf of California. The 



^02 



PHYSICAL GEOGRAPHY. 



I II ( ) 11 N I A 



CALIFORNIA 




Fig. 194. — Diagram of the Colorado 
Kiver Delta. 



former liead of the gulf, thus isolated from the rest, has been 
dried out, leaving the arid Coahuila basin in southernmost 
California, its central part being 300 feet below sea level. 

Sometimes a distributary of the Col- 
orado, called New river, turns north- 
west into the basin, forming a lake, 
as in 1891. If the lake rises high 
enough, it overflows southward along 
the western margin of the delta, this 
outlet being called Hardy's Colorado ; 
but as a rule its channel is dry. 
LOWER f ■^■"^ 

On the desert slopes of the 

Andes in western Peru nea,rly all 
the population is gathered on the 
flood plains of rivers that descend 
from the mountains to the Pacific. 

Some of the rivers, like the Piura in northern Peru, run 

dry for part of 

the year. When 

the wet season 

comes, travel- 
lers from up 

the valley are 

anxiously asked 

if the river is 

beginning to 

flow. As its re- 
freshed stream 

approaches the 

town of Piura, 

bands of people go out to meet it, marching back with its 

advancing current and celebrating its arrival by a public 




Fig. 195. — A Kiver VaUey in Desert Mountains, Peru. 



CLIMATIC CONTROL OF LAND FORMS. 



303 



holiday. All the fields and gardens of the valley are 
watered by canals led from its channel. 

Bad Lands. — When fine-textured, unconsolidated de- 
posits, such as lake silts, suffer dissection in an arid 
climate, they acquire an extremely irregular surface; 




Fig. 196. — Bad Lands. 

hence their name, bad la7ids, originally applied on account 
of the difficulty of travelling over them. The absence 
of vegetation allows the formation of numerous rivulets 
when rain falls. Every rivulet carves a channel, thus 
dissecting the surface in minute imitation of a maturely 
dissected plateau. 

The bad lands of South Dakota and Wyoming are best 
developed near the branches of the Missouri river system ; 
the wet weather streams here actively dissect the uplands 
in which the larger rivers have entrenched their valleys. 
As the rainfall is light, vegetation is almost absent and no 
loose soil remains on the dissected surfaces ; all the loosened 
waste is washed into the valleys of the chief rivers. 



304 PHYSICAL GEOGRAPHY. 

During the third quarter of the nineteenth century, the 
Sioux Indians made use of these bad-land districts as natural 
fortresses, in which pursuit was difficult ; here were fought 
some of the last battles in the unhappy warfare of settlers 
and soldiers against the native tribes. 

Interior Drainage Basins. 

Continental Interiors. — Regions situated far inland, 
remote from moist sea winds, receive light rainfall. In 
such regions a warping of the earth's crust or a mountain 
folding may produce great or small basins faster than the 
feeble rivers can fill them with water or waste, and may 
raise high barriers faster than rivers can cut gorges through 
them. 

It is in good part for this reason that the rivers of 
continental interiors so often discharge their waters into 
enclosed depressions, and fail to reach the sea. On this 
account, as well as because of diminished volume, the 
rivers of arid regions are largely busied in building up 
their lower courses. 

The interior basins of Utah, ISTevada, Arizona, and Mexico, 
having light rainfall, fail to support vigorous rivers. Warp- 
ing and faulting of the earth's crust in this region has pro- 
duced many enclosed basins, from which the rivers might 
easily overflow under a more generous rainfall ; hence the 
name. Great Basin region. 

Many streams descend from the mountains of the basin 
region and wither away on the sloping waste plains, failing 
to unite in a trunk river along the trough line between the 
ranges. Where the streams are a little stronger, a feeble 
trunk river may be formed, only to wither away as it flows 
toward the lowest part of its basin. 



CLIMATIC CONTROL OF LAND FORMS. 305 

Salt Lakes. — An interior basin receiving a moderate 
water supply will contain a lake in its lowest part. The 
lake, having no outlet, must have such an area that 
evaporation from its surface shall equal the supply from 
inflowing streams. Lakes of this kind are usually salt, 
for all the saline substances gathered in small quantity 
by the inflowing streams accumulate in the lake and may 
in time constitute a fifth, or even a third, by weight of 
the lake contents. 

Great Salt lake of Utah, with about 18% of salt, is of 
this kind, lying on the lowest part of the waste plain that 
has been built up in the depression among several mountain 
ranges. Its waters are so dense that a man's body will not 
sink beneath the surface. The Dead sea, with 24 <^ of salt, 
is one of the most famous salt lakes, occupying a long, 
narrow depression in Palestine; its surface is 1300 feet 
below the level of the Mediterranean. Lake Van in east- 
ern Turkey, containing 33% of salt, is the densest water 
body known. 

As the inflow of salt lakes is disposed of by evaporation, 
their depth and area vary with change of weather and season. 
When their shores are flat, as is usually the case, the shore 
line may shift several hundred feet between the wet and the 
dry seasons ; the strip of land laid bare at the low water 
stage is charged with salts ; it may bear a peculiar vegetation 
or may be covered with a saline incrustation. 

Unlike lakes among mountains, salt lakes lying in shallow 
basins surrounded by arid plains are not elements of beauty 
in the landscape. Settlements are seldom made on their 
unattractive shores. An explorer describes Lake Shirwa in 
southeast Africa as a shallow sheet of foul salt water, lying 
in the flat central depression of extensive alluvial plains, its 
margin occupied by great malarial marshes. All the unpleas- 



306 PHYSICAL GEOGRAPHY. 

ant features of a torrid quagmire are accented around its dis- 
mal shores, where crowds of flamingoes, cranes, and screaming 
water birds, jostling one another for room, only add to the 
depressing nature of the scene. 

Playas. — In interior basins where no permanent lakes 
occur, the larger rivers may, at time of flood, reach the 
lowest depressions and there spread out in shallow tem- 
porary lakes, which soon disappear in clear and warm 
weather. The silt brought by such rivers is spread over 
the depression and thus forms a broad plain of remarkably 
smooth surface, called a playa. 

One of the largest playas in the Great Basin region is 
known as Black Rock desert (i>, Pig. 205), in northwest 
Nevada. It measures about 100 miles in length by 12 or 15 
miles in breadth. It is overflowed in winter by the extension 
of Quinn river ; but so level is the plain that the playa lake 
is seldom more than a few inches deep. The wind stirs the 
water and raises the fine silt of the plain, making the water 
turbid ; the lake is then hardly more than ^' a vast sheet of 
liquid mud." In summer the playa is smooth and dry, hard 
baked by the sun, and perfectly barren ; one of the most 
desolate and monotonous surfaces in the world. 

Salinas. — Certain basins that formerly contained salt 
lakes have now been more or less completely dried out, 
leaving marshy or dry plains of salt, known as salinas, in 
the central depressions, avoided by all plant and animal 
life. 

The Bolivian tableland, a lofty waste-filled basin lying 
between two great ranges of the Andes, holds Lake Titicaca in 
its northern part at an altitude of 12,500 feet. The outlet 
flows 100 miles southeast to a shallow marshy salina about 



CLIMATIC CONTROL OF LAND FORMS. 307 

50 miles long. The water not evaporated here flows south- 
west and is lost in a broad salina of dazzling white surface. 
Somewhat further south is a more extensive salina, 4000 
square miles in area, a white and level plain covered with 
a layer of salt about 4 feet thick, impassable when wet, but 
firm in the dry season. 

Salt lakes and salinas yield common salt and other min- 
erals of commercial value. Great Salt lake is estimated to 
contain 400,000,000 tons of salt. These products would be 
of greater utility if they did not so generally occur in thinly 
populated, desert regions. 

The Development of Interior Basins. — Like young 
mountain ridges, where little carving has been done on 
uplifted blocks, young basins have received little waste 
from their rims. Alluvial fans have begun to grow for- 
ward around their margins, and the finer waste is spread 
to a moderate depth over their floors. 

The bottom of the trough occupied by the Dead sea is about 
2600 feet lower than the level of the Mediterranean. Ravines 
in the border of the uplifted plateau on the east lead down to 
stony fans that are advancing into the sea. But the great 
depth of the water, and the moderate extension of the fans 
show that the basin contains much less waste now than it will 
in the future. 

Interior basins enclosed by deeply dissected mountains 
have received the waste that the inner slopes of the 
mountains have lost. The floors of the basins have in 
this way been built up and smoothed. By the wearing 
down of the mountains and the filling of the basins the 
relief of the region as a whole has been decreased. 



308 



PHYSICAL GEOGRAPHY. 



Large alluvial fans of coarse waste with distinctly sloping 
surface are characteristic features of well-filled arid basins. 
The head of the fan may rise 500 feet above its rim, and its 
slope may stretch 10 or 15 miles forward from the mountain 
valley in which it heads. Thus these arid valleys, like lake 
basins in moister regions, are gradually being filled with 
delta-like accumulations of waste. 




Fig. 197. — The Waste-Filled Floor of Death Valley, Southeastern California. 

The water of mountain torrents is often completely lost in 
the coarse waste of the fans, whose deeper parts thus gather 
much ground water. By driving tunnels near the base of 
the fans the water may be reached and brought out to irri- 
gate the lower slopes. This method has been used for cen- 
turies in Persia and northwestern India. It is now employed 
in southern California, where fans of great size are formed at 
the base of the mountain ranges. 

When many neighboring alluvial fans are spread forth 
at the base of arid plateaus and mountains, they unite in 



CLIMATIC CONTROL OF LAND FOBMS. 



309 



a long gravel-covered slope resembling a river-made plain, 
but of steeper descent. The surface becomes less and 
less steep, and the waste less coarse, the farther the slope 
extends forward. 

Extensive stony slopes of this kind occur in the depres- 
sions between the desert mountains of Utah, Nevada, and 
Arizona. The waste fills the depressions to great depths, 
and backs up 2000 or 3000 feet on the flanks of the 
mountains. 




Fig. 198. — Half-Buried Uountain Bange, Nevada. 

If the depression between the mountains is of small 
breadth, the gravel slopes grow forward till they meet 
in a rather well-marked trough line ; here a stream may 
flow in the wet season. If of great breadth the slopes 
grade into a dreary plain, with occasional springs around 
its margin and temporary lakes in the center. 

Opposite the mouths of canyons, trains of coarse waste, 
including boulders weighing many tons, are spread forward 



310 



PHYSICAL GEOGRAPHY. 



by floods from cloud-bursts in the mountains — " immense, 
sudden, deluging rainstorms, which, at rare and exceptional 
moments discharge their waters into one of these mountain 
gorges. On such occasions boulders 6 or 8 feet in diameter 
are swept down the canyon in a fearful rush, and are some- 
times carried out on the ... slope for half a mile." At other 
points the slope is trenched from 50 to 200 feet deep opposite 
the canyons, revealing its stony structure. 

The farmer ant is one of the most remarkable and numer- 
^.-__ ous of the few forms 

of animal life on these 
stony slopes in the 
southwestern United 
States, near the Mexi- 
ca,n boundary. Each 
"farm" includes a 
clean threshing floor, 
from 5 to 30 feet across, 
with a belt of grass 
around it, and a passage 
to the underground 
dwelling in the center. 
"Roads" a foot wide 
connect the "farms" across the grass rings for hundreds of 
feet ; the " farms " may cover nearly all the surface over 
scores of square miles. 

In such a farming district other plants, common in the 
surrounding region, are carefully kept out by the ants. The 
grass is their food crop, as they live on its seeds. If the crop 
failed, they would die of famine by millions. The grass 
would greatly decrease if it were not cultivated and the other 
plants destroyed. 

As the waste from the higher enclosing mountains is 
washed into great interior basins, the smaller ridges may 
be nearly or quite buried. Many small basins, originally 




Fig. 199. — Home of the Farmer Ant. 



CLIMATIC CONTROL OF LAND FORMS. 311 

separated by ridges, may thus be converted into a few 
large basins ; in time all the basins may unite in a single 
depression, which will then receive the drainage and 
waste from all the surrounding region. 

A great part of Persia consists of large basins enclosed by 
mountains and without outlet to the sea. Long waste slopes 
stretch forward 5 or 10 miles with a descent of 1000 or 2000 
feet, stony near the mountain flanks, and gradually becoming 
finer-textured and more nearly level. The central depressions 
are absolute deserts of drifting sands, with occasional saline 
lakes or marshes. The population gathers around the margin 
of the basins where water is still to be found, avoiding the 
rugged and barren mountains on the one hand, and the unin- 
habitable central plains on the other. 

Central Asia repeats the same conditions on a still larger 
scale. The basin of Eastern Turkestan includes many half- 
buried ranges in its central part. It is quite possible that 
some ranges are completely covered with waste. Many rivers 
flowing from the mountain rim wither on their way towards 
the chief central depression ; only the largest river (Tarim) 
reaches it, there spreading out in Lob (Lake) Nor, The chief 
settlements are near the border of the basin, where the larger 
rivers come out from the mountains. 

Outward Drainage of Former Interior Basins. — The 

lofty desert plateau of Tibet consists of many mountain 
ranges Avith waste-filled basins between them. As in all 
such forms, the gradual wasting of the ranges and filling 
of the basins tend to make the whole surface more nearly 
level. In time a lofty plain might here be formed, stand- 
ing at a great altitude above baselevel. 

During the advance of this long process, the active 
headwater streams on the outer slopes of the enclosing 



312 



PHYSICAL GEOGRAPHY 



mountains may gnaw their way through the ranges, and 
thus capture some of the streams of the interior basins, 
giving them an exterior discharge. 

One of the lofty basins on the southern border of Tibet is 
now deeply dissected by the streams that have been turned 
outward to the deep valleys of the Himalaya in this way. 
Other basins (A, Fig. 200) are encroached upon by the head- 




Fig. 200. — Diagram of Outward Drainage of Interior Basin, Himalaya. 

water torrents (T) that have already gnawed their way 
through the northernmost range of the Himalaya (S). The 
deep notches thus worn in the mountains form the passes by 
which the plateau of Tibet is reached from th'e Himalayan 
valleys (F). 

An interior basin may gain exterior drainage when its 
depression is filled with waste until overflow occurs at 
some low point on the basin rim. Then the outflowing 
streams will tend to erode their channels with respect to 
the general baselevel of the ocean surface, instead of with 
respect to a central lake or playa ; and the basin will be 
worn down instead of built up. As the waste is washed 
out of the basin the rock floor will be worn down also. 

An arid region in southern Arizona and northwestern 
Mexico (the Sonoran district) includes forms that may be 



CLIMATIC CONTROL OF LAND FORMS. 



313 



explained in this way. A long rock-floored inclined plain 
(QJ}i, Fig. 201), descending 200 or 300 feet to a mile, leads 
forward from the base of the mountains (BQ). The gravelly, 
waste from the mountains is washed across the plain to a flat 
trough (NM), and the finest waste is washed along the trough 
to the sea. 




Fig. 201. — Diagram of a Waste-Filled Trough. 

It is thought that at an earlier time, when the mountains 
were much, higher (like KLH), the trough at their base was 
broadly filled with their waste {HJ)- At that time they 
resembled the mountains of Utah and Nevada, and the troughs 
did not overflow. An overflow of waste being after a time 
reached, the surface was gradually worn down lower and 
lower, and LHJ was changed to BQN. 



Sheetfloods. — ■ The behavior of the drainage in the Sono- 
ran region is peculiar. The rainfall averages only two or 
three inches a year ; for although a single shower may yield 
almost as much as the annual fall, the showers are very 
rare ; the sky is cloudless for a great part of the time. In 
the mountains the rainfall gathers in streams in steep-sided 
ravines, and issues upon the plains heavily charged with 



314 PHYSICAL GEOGRAPHY. 

waste. There the water finds no channels ; it spreads out in 
a shallow sheet, called a sheet flood, which gains a breadth of 
a mile or more, but a depth of only one or two feet ; rushing 
down the incline towards the troughs, but rapidly dwindling 
when it encounters layers of gravel on the rocky floor. 

As the sheetflood subsides, its waste is left strewn over 
the smooth rocky floor, and the ground water soon escapes 
by evaporation. Another storm, shedding its rain here or 
there upon the rock-floored inclines or on the flat troughs, 
washes the waste along a little distance ; and thus by degrees 
it is carried forward, at last reaching its goal in the sea. 

The Effect of the Wind ox Land Forms. 

Comparison of Winds and Streams. — Where the land 
surface is covered with vegetation, the wind has little 
eifect on the form of the ground. In arid regions where 
vegetation is scanty or wanting, the wind may become a 
powerful agent of denudation and transportation. In such 
regions the whole surface over which the wind acts should 
be compared to the uneven bed of a broad river. 

The difference of wind action on a dusty road and on a 
grassy field may be taken to illustrate the contrast between 
wind action in regions of dry and regions of wet climate. 

In a general way, the wind raises the finest dust into 
the body of its current, drifts along the sand at the bottom 
of tlie current, and rasps the unmoved stones and ledges 
with the drifted sand. 

The wind that blows over desert mountain tops sweeps 
away the finer waste so quickly that there is never enough 
of it to make the upper air dusty. On arid lowlands the dust 
is blown here and there ; what is raised by one storm hardly 



CLIMATIC CONTROL OF LAND FORMS. 315 

settles before another storm occurs; here the lower atmosphere 
is often turbid, the sky is of a dull gray color, and distant 
objects are obscured. 

Uplands, projecting into the great air currents, are 
stripped of their sand and dust, leaving their surfaces 
bare and stony. Less exposed surfaces gather the drift- 
ing sand in hills, called dunes. The finest dust is carried 
furthest and settles chiefly in protected basins, where the 
wind tends to stagnate. 

Many points of similarity may thus be found between wind 
and water action. The uplands of the Sahara have extensive 
surfaces of bare rock or of loose wind-carved stones; the dust 
and the finer sand have been blown away to settle on the 
lower lands. The stony uplands in the desert south of 
Algiers are known as hainniada, on which travelling is diffi- 
cult and fatiguing. 

Sand Dunes in deserts may grow to a height of from 
500 to 600 feet. In a region of relatively steady winds 




Fig. 202. — Sand Dunes in the Sahara. 



the sand is blown up the Avindward slope and carried over 
the crest; hence the dune may slowly advance, gradually 
changing its place and form. 



316 



PHYSICAL GEOGRAPHY. 



Drifting sand gives a loose footing and makes travelling 
in a desert a weary task. A hot and violent wind, known 
in Arabia and the Sahara as the Simum, raises clouds of 
sand and dust, rapidly modifying the form of the dunes 
over which it blows. It sometimes overwhelms caravans 
— the easier if men and beasts are already exhausted by 
thirst and fatigue. 

The San Luis valley in Colorado and New Mexico is a waste- 
filled basin enclosed by mountain ranges. It is an oval plain, 
measuring about 40 by 140 miles, at an elevation of from 7500 
to 8000 feet. The greater part of the surface is "as flat as a bil- 
liard table." Coarse gravels slope inward around the border ; 
streams wither as they flow towards the center ; fine silts floor 
the central area, where small alkaline lakes occur. Drifting 
sands, gathered from the basin, form extensive dunes on the 
eastern or lee side of the plain at the base of the enclosing 
mountains. A large lava flow covers many square miles near 
the southwest margin. The Rio Grande receives the stronger 
inflowing streams, and escapes southward through a deep and 
gloomy gorge in the mountains. 

An extensive dune-covered area is found in northwest 
Nebraska, occupying thousands of 
square miles. "The scenery is 
exceedingly solitary, silent, and 
desolate." The round hilltops rise 
evenly as far as the eye can reach ; 
travelling over them is extremely 
difficult. A scanty vegetation in 
the hollows, where ground water can 
be reached by plant roots, once supported great herds of buffalo, 
and now yields light pasture to wandering herds of cattle. 

Dust Plains. — During times of high wind the air of arid 
basins may be so darkened with dust as completely to hide 




Fig. 203.— Buffalo. 



CLIMATIC CONTROL OF LAND FORMS. 



317 



the sun. The finest dust penetrates all enclosures and 
makes everything feel gritty. As the winds decrease, the 
sun becomes visible, at first of a ruddy color ; it may 
disappear again in the murky atmosphere before reaching 
the horizon. 

The long-continued action of winds blowing from an 
arid continental interior may form heavy deposits of dust 
on the lower lands to leeward. Hills and valleys are in 
time buried hundreds of feet beneath the even surface of 
the dust plain. Such deposits are known as loess (a German 
word meaning loose ; pronounced almost like less). 

There are many loess-filled basins in the interior of China. 
Their margins, conta,ining gravel and sand washed from the 
enclosing slopes, are 2000 or 3000 feet higher than the 
central parts, 
which are occu- 
pied by playa 
muds or saline 
deposits. But the 
greater part of the 
basin is filled with 
a fine, almost im- 
palpable dust to a 
depth of hundreds 
of feet. 

Some of the 
loess-filled basins 
of China are now 
partly dissected ; 
a main river runs through the middle of the basin and receives 
branches that have worn a labyrinth of forking ravines in the 
loess deposits. 

Millions of Chinese live on the valley floors of dissected 
basins of this kind ; for loess is extremely fertile where well 




Fig. 204. —Loess Beds, Yellow River Basin, China. 



318 PHYSICAL GEOGRAPHY. 

watered. Great numbers of the people inhabit cave-like 
dwellings excavated in loess bluifs ; in a thickly populated 
district not a house may be seen. The yellowish color of 
loess prevails everywhere. It gives color and name to the, 
great river of the region and to the sea into which the river 
flows. 

Dry Regions, formerly Moist. — In certain regions, now 
arid, marks of a former moist climate are found. The dry 
valleys or wadies in the Sahara seem to be the work of 
larger and steadier rivers than now follow them. Certain 
basins now almost without water have been filled with 
great lakes, even to overflowing ; the former shore lines 
of the lakes are marked b}' cliffs, beaches, and deltas, and 
an outlet is sometimes traceable in a trench across the 
lowest pass in the enclosing highlands. 

The basin of Great Salt lake in northwestern Utah once 
contained a much larger lake, to which the name of an 
explorer, Bonneville, has been given. Its shore lines are 
still plainly recorded on the mountain sides nearly 1000 feet 
above the desert plain around the present lake ; the fore- 
ground of Fig. 103 shows extensive beaches of this lake. 
The channel of an outlet leads northward across a pass to 
the basin of Snake river ; hence the former lake must have 
been fresh. The change from the moister climate of Lake 
Bonneville time to the drier climate of to-day has caused the 
almost complete disappearance of the lake waters, revealing 
the sediments of the lake floor in an arid plain. The ancient 
lake deltas are now trenched by the streams that built them. 

One of the most remarkable features of this change of 
climate is its rapidity as compared with the changes of land 
forms. The cliffs, beaches, and deltas on the shore lines of 
the extinct lake are still remarkably distinct. The same is 



CLIMATIC CONTROL OF LAND FORMS. 



319 



true of a former extensive lake (Lahoutan) of very irregular 
outline in western Nevada, as well as of similiar ancient 
lakes in various parts of the world. 




Fig. 205. — Lakes Bonneville and Lahontan. 



The causes of climatic changes of this kind are little under- 
stood, but their geographical consequences in replacing exten- 
sive lakes among forest-clad slopes by desert plains between 
arid mountains are of great importance. 



Plants and Animals of Aeid Regions. 

Forms of Life in Arid Deserts. — Plant and animal 
life is scanty or absent in arid regions, because of the 
difficulty of securing food and water. The dryness of the 
soil is unfavorable to plant growth. Leaves are small or 
wanting, and thus the loss of water by evaporation from 
the leaf surfaces is diminished. Thorns are commonly 



320 



PHYSICAL GEOGRAPHY. 




developed, like so many signs — "keep off " — as if to lessen 
the chance of injury to the plant in a region where liv- 
ing is so difficult that 
every aid must be 
summoned to protect 
life. 

Duringlong droughts 
an arid region may 
seem almost free from 
vegetation. If rain 
falls, small plants 
spring up everywhere, 
refreshing the surface 
with their green color 
but soon wit'jering 
away in the sr ;3eding 
dry period. \i.liis is 

Fig. 206. - The Yucca, a Desert Tree. particularly marked OU 

the borders of the subequatorial rain belts, where the ground 
may be bare and dusty in the dry season and covered with 
vegetation in the wet season ; as on the Llanos of Venezuela. 
On the desert slopes of Peru, where droughts may last four 
or five years without rain, plants soon spring up after a 
shower. These examples show that the plants of arid regions 
possess great vitality. 

The same thing is seen in the subtropical belts, but less 
distinctly, for there the rain comes in the cool season ; as in 
the Algerian Sahara. In continental interiors, where most 
of the rainfall is in smnmer, the wandering of nomadic tribes is 
largely determined by the search for pasture for their flocks ; 
as on the dry plains or stepi^ns north of the Caspian sea. 

The larger plants of arid regions are thinly scattered, 
leaving much bare surface. There is no striving for 



CLIMATIC CONTROL OF LAND FORMS. 321 

space, such as commonly occurs in well-watered regions, 
where plants of more active growth may crowd out the 
weaker forms. Dry regions seldom produce plants of 
economic value. Trees are small, and their wood is 
hard and knotted ; they cast little shade on the dry, bare 
ground. The sagebrush, so abundant on the arid western 
plains of the United States, finds no use except as an 
inferior firewood. 

The contrast between the open plant growth of dry regions 
and the crowded forests and jungles of the equatorial rain 
belt is very striking. The equatorial forest is gloomy, reek- 
ing with the damp smell of rotting vegetation. Gigantic 
trees rise high before branching ; lesser trees push their way 
upward, searching for every foot of vacant space. Thorny 
creepers and tangled undergrowth twine beneath in an intri- 
cate and impassable web. Objects near at hand are hidden 
from view. On the other hand the glaring light of the sun in 
the unclouded sky over a desert is tempered only by dust 
raised from the parched ground. If 
scattered trees or bushes can grow, 
they are usually too far apart to ob- 
struct the view. 

The animals of deserts are gen- 
erally of dull or gray color, not 
easily seen on the barren surface. 
Many of them are fleet in move- 
ment, like the antelope ; or of OTeat 

T , P I'ig- 207. -Camel. 

endurance under a small supply of 

food and water, like the camel. Those which are slug- 
gish are often venomous, like the scorpion and rattle- 
snake. 




322 PHYSICAL GEOGRAPHY. 

The People of Deserts. - — • The human inhabitants of 
arid deserts are few and miserable, as compared to the 
more favored races of the world. Their food supply is 
scanty and of little variety. Their arts are primitive, for 
raw materials are of few kinds. They possess strength 
and endurance, without which life would be impossible 
under the difficulties around .them ; they have a "keen 
intelligence for every advantage that their desert home 
affords, but they cannot rise above a low stage of devel- 
opment. 

Many of the wandering tribes are, by force of necessity, 
beggars and robbers. The struggle for existence is so severe 
with them that they and their animals are frequently on the 
verge of starvation. Yet so accustomed are they to their 
wretched life that they do not wish for the changes proposed 
by strangers. 

The Papago Indians of the Sonoran region, south of the 
Gila river, move from place to place with the failing and 
flowing of springs. They are noted for strength, speed, 
endurance, and abstinence. The Seri Indians, living in the 
desert on the border of the Gulf of California, have no horses 
and are noted as runners. 

In regions of favoring climate and more varied products, 
the manner of life of civilized people is so complicated by 
long-growing habits and customs that it may seem in many 
ways to be independent of geographical conditions. In the 
simpler life of desert tribes the force of geographical con- 
trol is more apparent, but not more real. 

Oases. — Fixed settlements in desert regions are almost 
entirely controlled by the occurrence of water. They are 
commonly made where springs or streams flow upon the 
open country at the base of uplands and mountains ; or 



CLIMATIC CONTROL OF LAND FOEMS. 



323 



near the ends of such streams, where they can be distrib- 
uted in irrigating canals ; or at points where ground 
water may be found in the nearly dry channels of with- 
ered streams. Such settlements are called oases in the 
Sahara, and the same name may be used elsewhere. 




Fig. 208. — El Rantara Oasis, Algerian Sahara. 

The barrenness of many deserts is due simply to their 
dryness and not to an unfavorable composition of rock or 
soil. Where springs or streams moisten the soil, grass and 
trees may grow naturally. If the surface can be irrigated, 
its productiveness may be increased so as to support permanent 
settlements. 



The contrast between a habitable spot and the surround- 
ing barrenness is so grateful that " an oasis in the desert " 
has come to serve as a poetic figure. But oases are only 
relatively delightful. Their water supply is often limited 
and impure ; their products are few in variety and small 



324 PHYSICAL GEOGRAPHY. 

in quantity ; their industries are primitive ; tlieir inliab- 
itants have to suffer the disadvantages of isolation as com- 
pletely as the people of islands. 

The oasis of Siwa, in the Sahara, 350 miles west of Cairo, 
"the first halting place on the great desert highroad to the 
west," is still little changed from its condition in ancient 
times. Seclusion seems to have bred mistrust, for stran- 
gers are looked on as intruders. They and their modern 
ways of doing things are unwelcome. 

The large and important oasis of Merv, northeast of Persia, 
has a population of several hundred thousand, gathered in 
many villages. The oasis is on a flat alluvial fan, formed 
and watered by the Murg-ab (-river). The river is divided 
into two distributaries, then into forty-eight smaller branches, 
and again into hundreds of irrigating canals. 

The inhabitants of an open country that has a sufficient 
rainfall, with plentiful ground water easily reached in wells 
and with numerous springs and streams, are free to settle 
almost as they like. They seldom realize the importance 
that a spring or small water course has in the life of 
dwellers in deserts. 

The occasional springs on the arid plateaus of Arizona are 
regarded as so important that their position is indicated on 
the government maps of that region. Travellers across the 
plateaus follow trails that lead from spring to spring. 

Ice Sheets and Glaciers of the Present. 

Glacial Climate. — Where the temperature is so low 
that the snowfall of the colder season is greater than the 
loss by melting in the milder season, a heavy cover of ice 



CLIMATIC CONTROL OF LAND FORMS. 325 

and snow many hundred feet thick is formed. The icy 
sheet slowly creeps from the place of chief supply to lower 
ground ; there it melts and the water runs away in 
streams. Its edge may enter the sea, where besides melt- 
ing it breaks off in large masses which float away as ice- 
bergs. These long-lived accumulations of ice are called 
ice sheets and glaciers. 

The change from snow at the surface to ice beneath is 
aided by water from occasional rains and from surface melt- 
ing. The water sinks into the deeper snow and there freezes. 
The ice thus formed is granular, and the motion of the mass 
is much aided by a slight slipping of grain on grain. 

During winter in the northern United States there are fre- 
quent examples of the formation of small, short-lived ice 
sheets, after a succession of snowstorms with prevalent cold 
weather and occasional thaws. Such an ice sheet is not thick 
enough to move ; but if it should grow year after year to 
a thickness of 1000 or more feet, it would slowly move 
from the region of greatest height and thickness to lower 
ground in a milder climate. 

Antarctic Ice Cap. — A few explorers of the far south- 
ern ocean have discovered a great ice sheet ending in cliffs 
that rise from 100 to 180 feet above the sea. No land was 
seen back from their top. 

Although as yet known only on one side of the South 
Pole, the ice sheet is thought to form a polar ice-cap, per- 
haps 1000 miles in diameter. There may be some land on 
which the cap rests ; but it is believed that much of it lies 
on the sea bottom. It must tend to thicken from snow sup- 
ply over its desert, plateau-like center ; but it slowly creeps 
towards the free sea margin, where great tables of ice break 
off and float away. 



326 PHYSICAL GEOGBAPHY, 

The Greenland Ice Sheet. — Greenland is covered by a 
lieavy sheet of ice, measuring about 1500 miles north and 
south by from 300 to 600 east and west. It has a slightly 
conv^ surface, and probably rises to a height of 9000 
feet in the central part. As far as explored, the ice con- 
ceals all hills and mountains except near the margin, 
where the sheet is thinner; here occasional rocky sum- 
mits rise above the surface like islands in a frozen sea. 
Descending gradually towards the coast, the ice either thins 
out on land, or advances along the valleys in branch-like 
arms or glaciers, some of which extend into the sea. 

Some of the Greenland glaciers are from 10 to 50 miles 
broad where they enter the sea. Their forward movement is 
from 20 to 50 feet a day. Many icebergs are formed of great 
fragments broken from their front. Xansen, the famous Arc- 
tic explorer, was the first to cross the ice sheet of Greenland 
(1888, in latitude 64i^°). Peary crossed northern Greenland in 
1892. The interior is a monotonous desert of snow and ice, 
now melting and becoming almost impassable, now freezing 
over or receiving a new layer of snow. Most of the surface 
is unbroken ; but near the margin, where the motion is 
faster in one part than in another, the ice is deeply fissured 
or crevassed. 

The only inhabitants of this great cold desert are a simple 
microscopic plant that sometimes gives a red color to snow, 
and a minute worm. The Eskimos of Greenland live on the 
narrow belt of land between the ice sheet and the shore. 

Alpine Glaciers. — Glaciers of the Alpine type flow in 
stream-like tongues from the valley heads between lofty 
peaks and ridges. The snowfall in the valley, increased 
by avalanches from the enclosing walls, is gradually con- 
verted into granular ice ; and the ice slowly creeps down 



CLIMATIC CONTROL OF LAND FORMS. 



327 



the valley, melting as it descends to a milder climate than 
that of its gathering ground. The end of a glacier may 
often reach far below the tree line and even approach fields 
on the floors of the larger valleys. 

In the upper valley reservoirs the snow surface is concave, 
sagging from sides to middle ; here movement is directed 
inward from the enclosing slopes. Standing in one of these 
reservoirs in clear 
weather, one may 
see only dark 
ledges and peaks 
that rise over the 
dazzling snow 
under a deep blue 
sky, --- all barren 
and silent. In 
the lower tongue 
of a glacier the 
ice stream is con- 
vex, and moves a 
little towards 
either bank as well 
as downward 
along the slope of 

J.1 vallpv ^'^" 209.— Eosegg Glacier in the Alps, 

A glacier moves faster along the medial surface line than 
at sides or bottom, thus resembling a river. The movement 
of Alpine glaciers is from 100 to 500 feet a year on the aver- 
age, about as fast as the point of the hour hand of a watch. 
Where the valley steepens, the motion is more rapid and the 
ice is irregularly broken. Its parts unite again on the next 
gentler slope, and the ice stream flows on as before. 

The Aletsch glacier is the longest in the Alps, measuring 
about 13 miles from head to end. Glaciers of much greater 
size occur in the Himalaya and in Alaska. 




328 



PHYSICAL GEOGRAPHY. 



Creeping glaciers press heavily on their beds, dragging 
rock waste beneath them and scouring the bed-rock clean 
and smooth. Loose grains and fragments of rock, dragged 
along by the ice, scratch and groove the smoothed rock 
surface. The rock waste thus scoured from the ice floor, 
as well as that torn from projecting ledges and received 
in rock slides and avalanches from surmounting slopes, is 
^P-^-' dragged or carried along 

P'^ by the ice and deposited 

around its lower margin 
or at its end. Great 
boulders may be trans- 
ported in this way. 

The Swiss name mo- 
raine is applied to various 
forms of ice-borne rock 
waste. That underneath 
the glacier is called 
ground moraine; it is 
firmly compacted by the 
pressure of the ice. The 
waste on the side of a 
valley glacier forms the 
lateral moraine. Where 
two glaciers unite, the 
adjacent lateral moraines 
form a single medial moraine. The rough heaps and ridges 
of waste deposited around the end of a glacier (or at the 
margin of an ice sheet) form the terminal moraine. Here 
the waste is often loosely deposited ; it may be laid down 
in beds by water running from the ice. Glacial drift 
is a more general term for waste moved by ice and ice- 
water. 




Fig. 210. — Viesch Glacier in the Alps. 



CLIMATIC CONTROL OF- LAND FORMS. 329 

Large glaciers are sometimes so heavily covered with 
moraines near their lower end that a plant-bearing soil is 
formed upon them. Pasturage is found for the flocks of the 
mountaineers in the Himalaya on certain grass-covered mo- 
raines overlying the ice. Some Alaskan glaciers bear large 
forests near their ends. 

Water received from side streams and supplied from melt- 
ing ice gathers beneath a glacier and issues from an ice cave 
at its end. The water is usually whitened by fine "rock 
flour " ground beneath the ice. 

The length of glaciers is found to increase and decrease 
slowly in successive years. For a time they lengthen or 
advance ; then they melt back or retreat ; the change 
being completed in the Alps in a period of about thirty- 
five years. This is believed to result chiefly from a varia- 
tion in the snowfall. 

A change of snow supply is sooner indicated by a vari- 
ation in the end of a short than of a long glacier ; hence 
all the glaciers of a mountain range do not vary together. 

These slow variations in the length of glaciers may be com- 
pared to the rapid variations in the length of streams that 
descend from, mountains and wither away on deserts. After 
each rain the streams advance for a time and then retreat. 
The change is seen first in the end of the short streams. 

An advancing glacier at first usually overrides the soil 
in front of it, overturning trees, if they stand in the way ; 
it slowly drags forward the waste as a greater weight of 
ice comes upon it, and at last grinds and smooths down 
the firm rock ledges. A retreating glacier, receding from 
the terminal moraine that was made at its greatest ad- 
vance, leaves a barren stony bed to be slowly invaded 



330 PHYSICAL GEOGRAPHY. 

by plants from neighboring slopes. Here the forms pro- 
duced by the ice in scouring the surface on which it moved 
may be conveniently studied. 

The chief regions of valley or Alpine glaciers are the 
Alps, the Caucasus, the Himalaya, and other lofty ranges 
of Eurasia ; the New Zealand Alps ; the southern Andes ; 
and the northern members of the Rocky mountains, from 
the Selkirk range of Canada to the St. Elias range of 
Alaska. 

The snowy Selkirk range, crossed in a high pass by the 
Canadian Pacific Railway, promises to become a center of 
glacier excursions in North America, like the Alps in Europe. 
The heavy snowfall of the St. Elias range feeds large gla- 
ciers, many of which descend into the sea, like the famous 
Muir glacier, now visited every summer by excursion steamers 
from Pacific ports. 

From the valleys about Mt. St. Elias itself the uniting 
glaciers form a great ice fan at the base of the mountains 
(in shape like a flat alluvial fan), known as the Malaspina 
glacier. It spreads 20 miles forward to the sea, with a front 
of 70 miles. Rivers issue from tunnels beneath the ice and 
build extensive stony deltas. Smoothed rock surfaces, for- 
merly covered and worn by the ice, are well exposed near 
the border of the glacier. 

The Work of Ancient Glaciers and Ice Sheets. 

The Glacial Period. — The study of existing glaciers 
is of much importance from the light that it sheds on 
the geographical features of certain regions where great 
glaciers or ice sheets existed during former periods of the 
earth's history. 



CLIMATIC CONTROL OF LAND FOBMS. 



331 



The time of the former extension of glaciers and ice sheets 
is called the glacial period. It must have been a time of 
lower temperature and greater snowfall than to-day. It 
included several epochs of extensive advance and retreat. 
Regions that have been ice-covered are said to have been 
glaciated. It is often convenient to refer to periods of time 
before, between, and after the chief glacial advances as pre- 
glacial, interglacial, and postglacial. 

The glacial period probably corresponded with the period of 
moister climate in those interior basins that recently (in the 
earth's history) contained great lakes. 



During the glacial period many glaciers in lofty moun- 
tains advanced far dov^n their valleys and overspread 
the adjoining lowlands. Terminal moraines, formed at 
the greatest advance of the glaciers or during their retreat, 
are now found in the lower valleys. Lakes often lie in the 
glaciated valley 
floors, as if the 
enlarged ice 
streams had 
scoured out their 
basins. 

Ancient gla- 
ciers occupied the 
valleys of certain 
mountains that 
now bear little 
snow ; as in the 
Rocky mountains t.- „,. ^, • , ,„ c- ^t ^ r. ,-, 

•J Fig. 211. — Glacial Moraines, Sierra Nevada, Califorma. 

of Colorado and 

the Sierra Nevada of California. Great glaciers descending 

from the high Sierra into the desert valley of Mono lake in 




332 



PHYSICAL GEOGRAPHY. 



eastern California built strong moraines forward from the 
mountain base. Twin lakes at the head of the upper Arkansas 
valley in Colorado are held within heavy terminal moraines. 
Around the border of the Alps the lower land near the 
outlet of the chief valleys is often enclosed for 10 or 20 miles 
from the mountains by a belt of hilly morainic ridges. The 
ancient glaciers that descended southeast from Mt. Blanc to 
the river-made plain of the Po built a huge terminal moraine, 
whose ridges rise from 1000 to 1500 feet above the plain, 
enclosing a great amphitheater. 




Fig. 212. — Glaciated Area of the Northern United States. 



The Highlands of Scotland, to-day without permanent 
snow fields, were occupied by great streams of ice during 
the glacial period. Large glaciers extended into the 
ocean, east and west. The many lakes that lie in the 
broader valleys result partly from the scouring or erosion 
of the valley floors by the ancient glaciers, partly from 
dams formed by terminal moraines. 

The most extensive ice sheets of the glacial period 
were those that spread outward from the highlands of 



CLIMATIC CONTROL OF LAND FORMS. 



333 



eastern Canada across the basins of the Great Lakes upon 
the northern United States, and from the highlands of 
Scandinavia across the Baltic upon northern Germany. 

The occurrence of ancient ice sheets is known by the many 
marks of their presence still remaining, such as moraines and 
other forms of drift, transported boulders, and scratched rock 
ledges. The ice sheet that spreads from the highlands north of 




Fig. 213. — Diagram of an Ice Sheet. 

the St. Lawrence is known as the Laurentian glacier. It was 
a desert nearly as extensive as the Sahara. The Scandinavian 
ice sheet was nearly as large as the desert of inner Australia. 
These ancient ice sheets advanced and retreated more than 
once, reaching different limits in the successive advances. At 
each advance they drove away the plants and animals of the 
region that they invaded ; at each retreat plants and animals 
were free to take possession again of the uncovered surface. 



H M' L 




Fig. 214. — Diagram of a Retreating Ice Sheet. 

Effects of the Glacial Period. — The geographical conse- 
quences of the glacial period are numerous and important. 
Rivers flowing from the ice sheets were so well supplied 
with waste that they filled their valleys with broad grav- 
elly or sandy flood plains (A, Fig. 213). Since the disap- 



334 PHYSICAL GEOGRAPHY. 

pearance of the ice, the rivers have terraced the drift-filled 
valley floors {T, Fig. 214). 

The valleys of the south-flowing rivers of Ohio, Indiana, 
and Illinois, outside of the glacial area, are now bordered by 
drift terraces from 10 to 40 or more feet in height. The 
mounds that mark the sites of prehistoric Indian villages are 
frequently found upon these terraces. Many villages to-day 
have a similar situation. 

Not only at the time of greatest advance but also during 
the disappearance of the ice sheets, the valleys leading away 
from their retreating edge were generally more or less filled 
with washed sands and gravels. It was under such condi- 
tions that the Chippewa river of Wisconsin, heading in the 
retreating ice sheet and carrying much drift down its valley, 
built a fan delta in the valley of the Mississippi, obstructing 
the main river and causing it to spread over its flood plain, 
forming the narrow Lake Pepin (P, Fig. 219). 

The Connecticut and Merrimac valleys in New England, 
well within the glaciated area, have many drift terraces along 
their sides. The valleys must have been drift-filled while 
the ice was retreating ; the high flood plains thus formed 
have been trenched and terraced after the ice had disappeared. 

Terminal Moraines were generally formed along the 
margin of great ice sheets, not only at their furthest 
advance but also during pauses in their retreat (M, M', 
Fig. 214). The moraines are hilly belts of gravel, sand, 
clay, and boulders ; they may be one or more miles wide, 
and from 50 to 100 feet in local relief. Although seldom 
of conspicuous height, they are often the only hills to be 
seen for many miles in the prairie states of the Ohio basin. 
Their surface is often too uneven and their soil too coarse 
and stony for cultivation in competition with the fertile 
prairies that they interrupt. 



CLIMATIC CONTROL OF LAND FORMS. 



335 



Hollows or "kettles" among the morainic hills frequently 
contain small lakes or swamps. The small lakes of northern 
Indiana are of this kind ; their number is not less than 1000. 

Terminal moraines are strongly developed in the Dakotas. 
They are from 3 to 10 miles wide ; sometimes so rough, with 




Fig. 215. — Glacial Moraine*, North Dakota. 



so many stony hills and hollows, as to present a formidable 
barrier to travel. One may easily lose his way on this undu- 
lating surface, where the hills are all much alike and where 
no conspicuous landmarks serve as guides. 

Ground Moraines. — During the occupation of a region 
by an ice sheet, the terminal moraines receive only a 
small part of the rock waste that is dragged forw^ard by 
the slow motion of the ice or washed along by subglacial 
streams. A great part of the drift remains beneath the 
ice as a ground moraine, distributed over the glaciated 
region. It may be spread unevenly, causing irregular 
changes of moderate amount in the form of the surface. 
Where it accumulates in greater quantity, it may be of 



336 



PHYSICAL GEOGRAPHY. 



sufficient thickness to buiy low hills and shallow valleys, 
forming extensive plains. It is especially plentiful near 
the margin of the glaciated area. 

The ground moraine left by an ice sheet is an unsorted 
and compact deposit of rock waste. It is sometimes called 
" boulder clay " from containing many large rocks packed in 
a stony clay. It is known as "hard pan" to contractors, 
who find much greater difficulty in digging foundations or 
opening railroad cuts in the ground moraine than in the loose 
sands and gravels that were washed forward from the edge of 
the ice. The Scotch word till is the best general name for 
this deposit. 




Fig. 216. — An Esker. 



The hills and valleys of New England are irregularly 
sheeted over with compact ground moraine, here clog- 
ging a valley, there smoothly cloaking a hill, and again 
leaving a rocky surface bare. Mounds, ridges, and plains 
of washed sands and gravels are also common in the val- 




CLIMATIC CONTROL OF LAND FORMS. 337 

leys, the result of stream action at the margin of the latest 
ice sheet during its retreat. The ridges are called eskers. 

The till of New England contains many boulders, from 5 
to 20 feet in diameter, and sometimes so plentiful on the 
surface as to make agriculture impossible. Even where less 
numerous, the 
boulders must 
often be gathered 
from the fields and 
thrown into heaps 
or built into walls 
before plowing is 
possible. 

Northwest 

Ohio has been ng. 217.-AGlaeialBoulder. 

converted from a region of hills and valleys into a smooth 
plain by a heavy covering of till, at many points more 
than 100 feet thick, and averaging 30 or more feet over 
hundreds of square miles. 

The till of Ohio is less stony than that of New England. 
It furnishes good soil, for it consists of a thorough mixture 
of waste from many kinds of rocks, gathered under the ice 
and not exhausted by plant growth during its accumulation. 
The till plain of northwest Ohio is for this reason more fertile 
than the hilly country in the southeast part of the state, 
beyond the limit of ice action. The same is true of large 
areas in the northern central states as far west as the Dakotas. 

Shallow lakes or marshy tracts occur here and there on the 
till plains from Ohio to Minnesota. The streams of the region 
bear every mark of youth. They follow narrow valleys, and 
are frequently interrupted by falls where they have cut down 
through the till to the rocky floor. In Minnesota, lakes are 



338 PHYSICAL GEOGRAPHY. 

very numerous in hollows in the till and among the terminal 
moraines. The falls and rapids of the upper Mississippi are 
all of postglacial origin. Glacial action must have been com- 
paratively recent (not many thousand years ago) in these 
states, as the streams have been so little developed since the 
ice disappeared. 

In southern Iowa and northern Missouri there is an exten- 
sive sheet of drift, burying the rock floor for miles together. 
Here no lakes occur ; the numerous valleys are broad floored 
and well opened ; few falls interrupt the even reaches of the 
streams. The glacial epoch in which this well-dissected drift 
sheet was dragged forward must have been much less recent 
than that in which the smooth and undissected till plains of 
northern Ohio and Minnesota were formed. 

Drumlins. — In some glaciated districts the till was 
here and there gathered beneath the ice sheet in smoothly 
arched, oval hills called drumlins., commonly half a mile 





Fig. 218. — A Drumlin. 

or more long, and from 100 to 200 feet high, easily rec- 
ognized when once known. They may be compared to 
sand bars in rivers or to sand dunes under the wind, 
all such built-up mounds occurring where more material 
is brought than is carried further forward. 



CLIMATIC CONTROL OF LAND FORMS. 339 

Numerous drumlins occur within an area enclosed by a 
well-defined moraine in southern Wisconsin. Here the land- 
scape presents a succession of arched hills, with flat marshy 
plains between them. The streams wander along such courses 
as the drumlins allow. The preglacial stream courses cannot 
be determined, so heavy and extensive is the drift cover. 

Hundreds of drumlins are found on the Ontario lowland of 
western New York. On the uplands in central Massachusetts 
many drumlins are cleared and farmed, in preference to the 
more rugged rocky hills. Most of the islands in Boston har- 
bor are drumlins. Many hills of this kind are distributed over 
the lowland of Scotland between Glasgow and Edinburgh. 

Marginal Lakes. — When an ice sheet retreated from a 
land surface that sloped towards it, temporary lakes may 
have been formed in the depression between the land 
slope and the ice front (i, Fig. 214). The lake floors 
received layers of fine silt, forming smooth plains when 
laid bare after the disappearance of the ice. The shore 
lines were marked by cliffs, beaches, and deltas of greater 
or less size, now deserted by the waters that made them. 

One of the most extensive glacial-marginal lakes has been 
named Lake Agassiz. When at its greatest size, it stretched 
hundreds of miles northward from Minnesota and North 
Dakota into Canada. Its floor is in part a plain of till ; 
in part covered with fine silts, nearly as level as the sea. It 
is now traversed by the main stream and branches of the Red 
river, whose narrow valleys proclaim the extreme youth of the 
plain. Great wheat farms (Fig. 173) and pastures (Fig. 182) 
now profit from the fertile soil. 

The shore lines of the glacial Lake Agassiz are marked by 
wave-made beaches and by the deltas of inflowing streams. 
The latter are often so sandy that dunes have been formed on 



340 



PHYSICAL GEOGRAPHY. 



them by the winds. Following the shore lines southward, 
they converge and almost unite at a slight depression in the 

enclosing "height of 
land " ; here the lake 
outlet is found in a 
well-defined channel, 
a mile or more wide, 
lea.ding southeast to 
the Mississippi. The 
Minnesota river, a 
small stream in com- 
parison with the great 
current that once 
flowed from the lake, 
now wanders along 
the floor of the chan- 
nel. 




Fig. 219. — The Glacial Lake Agassiz. 



All the Great 
Lakes were tempo- 
rarily expanded while the retreating ice sheet obstructed 
their discharge by the St. Lawrence ; they rose for a time 
to higher levels and spread over the bordering lands. 
Their shore lines, marked by cliffs and beaches, have been 
traced for hundreds of miles ; their silted floors, bordering 
the present lakes, form many fertile prairies. 

When the northward discharge of Lake Michigan was thus 
obstructed, the overflow ran southwest across a low " height of 
land " to the Illinois river, and thus to the Mississippi. When 
the ice retreated further, and Lake Michigan gained an outlet 
through Huron, the waters sank to a lower level, and the for- 
mer outlet remained as a low notch, which was afterwards a 
" portage " for Indian canoes. The site of Fort Dearborn was 
thus determined ; and from this small beginning in a favorable 



CLIMATIC CONTROL OF LAND FORMS. 341 

situation between tlie East and the great Northwest the city 
of Chicago has grown. To-day the ancient lake outlet has 
been deepened by cutting an artificial canal ; a strong current 
flowing through it from the lake carries the drainage of the 
city to the Mississippi system. 

When the lower St, Lawrence was blocked by the waning 
ice sheet, the expanded Lake Ontario overflowed down the 
Mohawk to the Hudson. The outflow cut down a flat-floored 
channel at Rome, N. Y., and here is the ''long level" of the 
famous Erie canal, where no lock is needed for many miles. 
The beaches of the ancient lake shore are very distinct ; many 
of them are used as naturally graded roadways. 

The shore lines of the glacial-marginal lakes are no 
longer level, as they must have been 'when formed. They 
ascend a few feet in a mile to the northeast. Hence it 
must be concluded that the land has risen in that direc- 
tion during or since the retreat of the latest ice sheet. 

Eecent observations have shown that the tilting of the land 
is still in progress, causing a change of level of about half 
a foot in 100 miles in a century. 

A remarkable consequence is predicted if this change 
of level continues. In a few thousand years, before 
Niagara can lower the level of the upper Great Lakes 
by wearing back the great falls between Lakes Erie and 
Ontario, the uplift of the land in the northeast will have 
raised the lake waters of southern Michigan high enough 
to restore all the overflow to Chicago. Only Ontario will 
then remain in the St. Lawrence system, while the Illinois 
river will be greatly increased in volume. 

Lake Basins. — The drainage of a glaciated region is 
often greatly disordered by glacial action. At one i)lace 



342 



PHYSICAL GEOGRAPHY. 



a valley floor may be scoured out, producing a lake basin. 
At another the irregular distribution of drift may divert 
a stream to a new course, where it is now seen cutting a 
steep-walled young valley with many falls and rapids. A 
lake is often formed up stream from the drift barrier. 

The Adirondacks, a well-dissected and subdued mountain 
group, resemble the Black mountains of North Carolina in 
many features, but are contrasted with them in the possession 
of numerous lakes and in the frequent occurrence of gorges 




J^S£^h ^.' ' 



--^.^^-^ 






S:"r-"^ ' -■'~ 






Fig. 220. — Lake in the Adirondacks, New York. 

Q' chasms ") and falls along the course of the outflowiug 
streams. These peculiarities result from glacial action, which 
the Adirondacks suffered in common with the other northern 
parts of the country, but which the southern mountains 
escaped. 

Rapids and Waterfalls. — When a river carves terraces 
in its drift-filled valley, it often happens that the new 
course is entrenched on one side of the preglacial channel, 



CLIMATIC CONTROL OF LAND FOEMS. 343 

and thus the stream comes upon a buried ledge. Here a 
fall is formed; for the drift down stream is (relatively) 
soon washed away, while the ledge is cut down much 
more slowly. The valley is narrow where the river cuts 
a gorge in the ledge. The alternation of waterfalls and 
graded reaches in many northern rivers is thus explained. 

The Merrimac is a famous river of this kind. Its falls 
at Manchester, Lowell, and Lawrence have determined the 
growth of great manufacturing cities. Rochester, Grand 
Eapids, Minneapolis, and many other important cities have 
grown up at the side of falls on rivers that have been turned 
from their preglacial channels by glacial drift. 

Where drift is plentiful and the preglacial relief of hill 
and valley is moderate, rivers may be displaced far from 
their former courses. Niagara is one of the most remark- 
able examples of a large river on a new course ; the 
upland that it crosses is a form of preglacial origin (an 
upland of an ancient coastal plain), while the gorge and 
falls are postglacial and extremely young. 

It is probable that in preglacial time the region of the 
Great Lakes was drained by a large river that followed in 
a general way the main line of the St. Lawrence system ; but 
the precise course of this ancient river has not been deter- 
mined. Niagara is a new river, whose course was taken 
across the upland between the Erie and Ontario lowlands 
after the retreat of the ice sheet. At first the river fell over 
the northern bluff of the upland. But as the plunging water 
undermined the capping layers, the gorge was cut backward 
through them. The falls have now retreated about seven 
miles from their first position. An international boundary 
line here follows the accidental path of the postglacial river. 
A small fraction of the water in the river is now diverted 



344 



PHYSICAL GEOGRAPHY. 



from the falls and carried by a canal to supply power to 
factories, to drive electric cars, and to furnish electric light 
to cities. 

Moraines and other drift deposits, forming new divides, 
frequently cause important changes in the areas of river 
systems. The headwaters of the Mississippi in northern 
Minnesota are separated from Canadian drainage by drift 
hills, Lake Itasca being but one of the innumerable lakes 
held in drift basins, all of which are very modern features 
in this ancient river system. Where the Mississippi rose 
before the drift hills were formed, no one can say. 

The divide between the upper Ohio and the St. Lawrence 
systems is largely determined by moraines and drift barriers 
south of Lake Erie. The same is true of many divides 
and subdivides between the streams of the prairie states of 
Indiana and Illinois. 

Central Areas of Glaciated Regions. — The highlands of 
eastern Canada, whence the ice sheets moved out to the 



^ \fKr'-^-~..- 








Fig. 221. — Ice-Worn Kocks, Coast of Maine. 



surrounding regions, and where the ice must therefore 
have been of great thickness, possess relatively little drift. 



CLIMATIC CONTROL OF LAND FORMS. 345 

Much of the surface is occupied by bare rock, clean 
scoured, or by a thin stony soil. Here the action of the 
ice sheet was chiefly destructive ; while on the surround- 
ing region, as south of the Great Lakes, it was more 
largely constructive. 

Whatever soil the eastern Canadian highlands possessed in 
preglacial times has been stripped away; it now lies in the 
till plains and moraines south of the Great Lakes. The 
generally even surface of the highlands (a worn-down old- 
mountain region, somewhat dissected in preglacial time) now 
consists of low rounded hills of firm unweathered rock 
separated by shallow troughs that often hold lakes and 
swamps both large and small. Many of the lakes lie in 
eroded rock basins ; others are held behind drift barriers. 
The undeveloped character of the streams is an indication of 
the disorder in the drainage system produced by glacial 
action. 

The immaturity of the drainage of this region is imitated 
in a small way when the snow and ice of winter melt from a 
road, whose arched surface may be taken to represent the 
highlands. Innumerable pools find outlets- by irregular rills ; 
the rills have minute rapids on stony sills. During a rain on 
such a roadway, the rills may be seen to deepen their channels 
and lower the level of pools, or discharge them entirely; thus 
imitating the changes that are progressing with relative 
rapidity on the Canadian highland. 

The highlands of Scandinavia repeat many of these fea- 
tures, but their altitude is greater and their valleys are deeper. 
The innumerable small lakes and the rapids and falls in the 
streams of Sweden and Finland are all of glacial origin. The 
great depth of the Norwegian fiords is by some explained as a 
result of intense glacial erosion. 

The ice sheets of the glacial period have vanished from 
the northern United States and eastern Canada. The 



346 PHYSICAL GEOGRAPHY. 

Indians that occupied this region when the Europeans 
first landed have greatly decreased in number, disappear- 
ing entirely in the more thickly settled districts. The 
Indians are always considered in the study of American 
history. The vanished ice sheets are of even greater 
importance in American geography. 



CHAPTER XII. 
SHORE LINES. 

The Border of the Lands. 

Next to the prospect gained from a lofty mountain, 
the view of the sea from the border of a highland is 
the most inspiring sight that the earth offers. To the 
traveller from an inland country it is as if the shore line 
marked the beginning of a new kind of world. There is 
the mystery of the distant horizon, far beyond which 
strange lands are hidden. There is the unceasing move- 
ment of the waves as they roll upon the beach, and of the 
tides as they slowly rise and fall ; and the thought comes 
that thus the ocean has been rolling in waves, rising and 
falling in tides, ever since the lands and the waters were 
divided. With the sight of the vast ocean comes the 
thought of unending time. 

While the surface of the land has been for ages attacked 
by rain and rivers, the border of the land has been 
attacked by the sea. The sun warms the air in the torrid 
zone, and thus the general circulation of the atmosphere 
is established. The winds beat on the ocean and form 
waves ; and the waves run ashore and dash in surf upon 
the lands. The border of the land is worn back under so 
constant an attack, and the waste taken from it by the 
surf, as well as that washed into the sea by rivers, is 
slowly carried away into deeper water by the waves, the 



348 



PHYSICAL GEOGRAPBY. 



currents, and the tides. In time the area of the land 
would be greatly reduced by the invasion of the sea, were 
it not for upheavals of the earth's crust by which the 
land is now and then, here and there, renewed. 

The contour of the land border exerts a strong control 
on coastwise trade and on international commerce ; for 
the dangers of the sea are not so much in the storms and 




Fig. 222. — Sea Cliffs, Grand Manan, New Brunswick. 



waves of the open ocean as in the shoals and reefs of the 
shore. A rocky coast, descending in bold cliffs to a surf- 
beaten beach, is justly dreaded when storm winds blow 
landward. A safe harbor, protected from winds and 
waves, is eagerly sought for when a vessel nears the coast. 
The outlines of the shore deserve as careful study as the 
forms of the land. 



SHORE LINES. 349 

The Development of Shoee Lines. 

Classification of Shore Lines. — Where the margin or 
coast of the hmd dips under the sea, the water lies against 
it and marks the shore line. The original outline of a 
shore depends on the form that the land had when its 
present attitude with respect to the sea was taken. Various 
changes are afterwards made by the action of waves, cur- 
rents, rivers, and other agents. 

It lias been learned that in some parts of the world the sea 
borders upon a smooth coastal plain that was once a sea bot- 
tom (p. 118), and that in other parts it lies on the flanks of a 
depressed mountain range (p. 195) ; hence this chapter may 
be begun with an understanding that the attitude of the land 
suffers greater or less change with respect to the sea; and that, 
as the land rises or falls, the outline of the shore changes. 

It will now be shown that some idea of the time since the 
present attitude of a coast land was taken may be gained 
from the form of bars built by waves off shore from a coastal 
plain, from, the area of deltas built by rivers forward from 
their mouths, and from the height of cliffs cut by waves on 
headlands. 

Shore lines in their original form, unchanged by sea 
action, may be divided into two classes, according as 
they are produced by uplift or by depression of the land. 
The shore line is smooth and simple and bordered by 
shallow water, where the sea lies on an uplifted sea 
bottom. It is irregular and complicated and generally 
bordered by relatively deejD water, where the sea lies on 
a depressed land surface. Shore lines of the first class 
border lowlands of weak strata ; they are comparatively 



350 PHYSICAL GEOGRAPHY. 

liarboiiess and do not offer easy opportunity for traffic 
between land and sea. Those of the second class gener- 
ally have rocky headlands enclosing protected bays, where 
harbors and settlements are favored. 

There are exceptions to this simple classification. The sea 
bottom is sometimes uneven, as where a hilly region has been 
depressed. The sediments laid on such a sea floor accumulate 
chiefly in the deeper parts, and thus tend to reduce the imeven- 
ness of the bottom. If uplift occur before the bottom is 
well smoothed, the new shore line will be irregular, although 
belonging to the first class. 

Shore Lines of the First Class. — The low plain of 
Buenos Ayres dips gently beneath the sea, whose waters 
are shallow for many miles off the simple shore line. 
Large vessels cannot approach close to the land, except 
where an artificial harbor has been dredged out. 

When storm winds blow from the sea, they brush the water 
upon the low coast and cause destructive sea floods ; dikes are 
built along certain parts of the shore to keep the waters off. 

Sand Reefs. — Along the shallow shores of low lands, 
storm waves beat up the bottom sands and in time build 
off-shore sand reefs, enclosing long, narrow lagoons. Roll- 
ing surf beats on the outer beach of the reef, slowly grind- 
ing the sand finer and finer, and sweeping the finest 
particles far off shore ; but the reef is not easilj^ destroyed, 
in spite of its loose texture, for about as much sand is 
brought in from the sea bottom as is ground up on the 
beach and taken away. 



SHOEE LINES. 



351 



The slow movement of tidal or wind-driven currents along 
the beach gives it a straight or gently curved front. On-shore 
winds blow sand from the beach, and build sand hills or dunes 
of irregular form, sometimes 50 or 100 feet high, on the reef. 
The sand drifts into the lagoon, making the inner border of 
the reef somewhat irregular. Sediments are brought by streams 
from the land, and, with the aid of salt-water plants, the lagoon 
is gradually converted into a salt marsh at high-tide level, inter- 
sected by numerous tidal channels, as in Fig. 223, b, e. 




Fig: 223. — Diagrams of Coastal Plain Shore Lines. 

Along the coastal plain of Texas the mainland shore line is 
simple (except where interrupted by small bays caused by a 
very slight depression of the plain after shallow valleys had 
been cut in it). It is fronted by a sand reef, whose beach has 
a remarkably smooth curvature. Much of the lagoon behind 
the reef is only 5 or 10 feet deep. Galveston, the chief port 
of the state, is built on the reef (Fig. 238), in order that its 
wharves may reach deeper water than that of the lagoon, and 
thus gain the advantage of traffic by seagoing vessels. 



352 



PHYSICAL GEOGRAPHY. 



M&^'Q 



A peculiar series of sand reefs fringes the coastal plain of 
North. Carolina (the mainland shore line being indented by 
shallow " sounds " due to moderate depression of the region 
after the uplift and dissection of the plain). Here three long 

narrow reefs, with concave 
outline to the sea, unite in 
sharp angles pointing sea- 
ward and forming Capes 
Hatteras, Lookout (Fig. 
224), and Fear. The 
curved reefs appear to re- 
sult from the action of 
eddying currents between 
the continent and the Gulf 
Stream. Long sand shoals 

Fig. 224. - The Hooked Spit of Cape Lookout. trail off shorC f rom the 

capes, greatly endangering coastwise navigation. The reefs are 
locally known as the " Banks"; the few people living on them 
are called " Bankers." A small breed of horses, known as 
" Banker ponies," run wild on the reefs. In the absence of 
springs and streams, the ponies scrape away the sand until 
they reach fresh ground water. Many of them are sold for 
use on the mainland. 




Cape Lookout^ 
A T L A ]Sr Tl.C OCEAN 



Inlets. — The flow and ebb of the tides, reenforced at 
ebb by river discharge from the mainland, preserve open 
passages or inlets through the reefs (Fig. 225). The 
stronger the tides, the greater the number of inlets. 



On the Texas coast, where the range of the tides is small, 
there are few inlets ; one reef is unbroken for nearly 100 miles 
northward from the mouth of the Eio Grande. Traffic between 
land and sea is thus almost entirely cut off for long distances. 
On the New Jersey coast the tidal range is stronger, and inlets 
are more numerous. On the South Carolina coast the tides 



SHOBE LINES. 



353 



P;iP A jr /;, / c 
s f) ' I- ^' 1) 




are still stronger ; there tlie reefs are so frequently broken that 
they do not interfere with traffic between land and sea. The 
str on g tidal c ii r r e n t s 
maintain inlet channels 
deep enough for seagoing 
vessels to enter the har- 
bors of Charleston and 
Savannah. 

Tidal currents in in- 
lets sometimes cause so 
rapid a change in the 
form and depth of the 
channel that the inlets 
are left blank on sailing 
charts. Masters of ves- 
sels must then trust to Fig. zas.-ATidallnlet and Delta. 

local pilots to show them the best passage. The sand swept in 
and out by the changing currents forms shoals known as tidal 
deltas (Fig. 225) ; their outer edge forms a bar so shallow 
that vessels must often wait for high tide before crossing it. 

Advance and Retreat of Sand Reefs. — When sand is 
brought (from the bottom or from elsewhere along shore) 
in greater quantity than it is carried away, reefs broaden 
on the seaward side and slowly advance into the sea 
(Fig. 223, h). Reefs may thus grow to be a mile or more 
wide. They retreat when more sand is lost than gained, 
their dune sands slowly blowing back into the lagoon or 
upon the lagoon marsh (Fig. 223, c). At last the lagoon 
disappears, and the mainland is directly attacked and 
slowly cut back in a long low bluff (Fig. 223, d). 

At Atlantic City, a seaside resort on a sand reef in southern 
New Jersey, the reef is broadening and gaining on the sea. 
Some of the hotels facing the beach have been moved forward 



354 PHYSICAL GEOGRAPHY. 

SO as to keep near the ocean front. Further north the' Kew 
Jersey sand reefs are retreating ; for tide-marsh mud, matted 
by lagoon plants, is foimd on the outer beach (Fig. 223, c). 

Still further north the sand reef is absent, and the mainland 
is cut back in a low blirff on which Long Branch, a noted 
resort, is built. Severe storms cut away the base of the 
bluff, sometimes undermining the houses above. 

The low coast of the middle Netherlands has retreated 
two miles or more in historic times ; for although the 
attack by the sea is not so vigorous as on a coast exposed 
to the open ocean, the land offers little resistance to the 
waves and tides. A belt of dunes, half a mile or more 
wide, lies inland from the smooth harborless beach. The 
chief ports are on the lower courses of rivers, whose chan- 
nels are broadened by the tides. 

The Eomans built a castle back of the dunes, near the 
mouth of the Rhine. In 1520 the dunes had blown inland, 
grain by grain, leaving the castle close to the sea. In 1694 
the castle stood in the sea, about half a mile from land. In 
1752 it disappeared, destroyed by the waves. 

In 1460 a church that had been built inside of the dunes 
in the Dutch village of Scheveningen (near The Hague) was 
reached by the sea. A new church was then built about a mile 
inland, at the east end of the village. In 1574, the outer part 
of the village having been gradually consumed by the waves, 
new houses had been built east of the church, so that it stood 
in the middle of the village. In a later century the new 
church stood close to the shore, the body of the village having 
moved beyond it. 

Lake Shores. — Although the waves and currents of 
lakes are weaker than those of the sea, their shores never- 
theless exhibit all of the features above described for 



SHORE LINES. 



355 



the shores of the sea, with the exception of those clue 
to tides. 

The shores of the Great Lakes have wasted sufficiently to 
develop bluff's or low cliff's of comparatively even front for 
distances of many miles ; as along the southern shore of Lake 
Erie, west of Buff'alo. Many other features of lake shores 
imitating those of seashores might be mentioned. 

Coastal Plain Cliffs. — As the margin of a coastal plain 
is cut back by the sea (Fig. 223, d), and' the shore bluff in- 
creases in length and height, longer and longer stretches 




Fig. 226. — The Sea Cliffs of Normandy. 



of the shore become harborless ; but it is seldom that 
coastal plains terminate in cliffs of great dimensions. 
Hence it must be inferred that uplift or depression of the 
land generally occurs, interrupting the regular develoiD- 



356 



PHYSICAL GEOGRAPHY. 



merit of shore features before the sea has had time to cut 
far back into the continent. 

An exceptional case is found in northwestern France, 
where the upland plain of Normandy (in general structure 
similar to that of ancient coastal plains) fronts the sea in a 
vertical sea cliff, 200 or 300 feet high, with gently curving 
shore line for many miles. A large part of the plain must 
have been consumed by the sea in the development of the 
cliff. 



The sea and land are here separated as if by a wall. The 
plain is cultivated by its agricultural population close to the 

top of the cliff. So 
much land has been 
cut away that the lower 
trunks of many rivers 
have disappeared, leav- 
ing the upper branches 
to enter the sea as inde- 
pendent streams, as in 
Fig. 227. The valleys 
of the smallest streams 
end in the cliff face, and 

iiS. 227. - valleys in the CUffed Uplands of Normandy. ^j^^ gtrCamS fall tO the 

beach below. Larger streams have cut their valleys down to 
sea level, opening little harbors ; here alone are villages built 
close to the shore line. The stream harbors are kept open 
with difficulty, on account of the plentiful sand and cobbles 
that drift along the beach. 

There is good reason for believing that Great Britain has 
been separated from the continent of Europe in great part by 
the retreat of the sea cliffs on each side of the English 
channel. Wolves and other large animals that formerly lived 
in England as well as on the continent imply the existence of 




SHORE LINES. 357 

a land connection, as they could not have crossed the waters 
of the channel, and it is not probable that they were carried 
across by man. 

Effects of Depression and Elevation. — Depression of 
the land may interrupt the orderly progress of seashore 
action at any stage in the development of shore lines of 
the first class. The sea then advances upon the lowland, 
entering furthest along the valleys and thus producing a 
shore line of the second class, but with moderate coastal 
relief, upon which a new series of changes takes place. 

The irregular shore line, with many sounds and bays along 
the Atlantic coast from North Carolina to New Jersey, is a 
good example of the effect of depression. Farmers would 
have occupied the valley floors if the low land had not been 
drowned; now fishermen gather from the bays "the harvest 
of the sea." 

Movements of elevation are as common as those of 
depression, but their effects are generally less apparent. 
The sea, retreating from its former position, begins the 
development of a new shore line. The former shore line 
may be marked by low ridges of sand reefs and dunes, or 
by bluff-like terraces if an advanced stage of development 
had been reached before elevation. 

A low bluff, interpreted as a former shore line, has been 
traced on the low coastal plain of Virginia and North Carolina 
a short distance inland from the present seashore. Further 
study will probably discover many more examples of this kind 
on the Atlantic coastal plain. 

The coastal plain of Mexico is not a perfectly smooth 
inclined plain, but is benched by several low terrace-like steps, 
which are believed to mark the action of the sea during pauses 
in the elevation of the region. 



358 



PHYSICAL GEOGRAPHY. 




Fig. 228. — Diagram of an Irregular Shore Line. 



Shore Lines of the Second Class. — The variety of 
shore features here included is greater than in the first 

class, because 
the forms of 
the land are 
more varied 
than those of 
the sea bottom. 
When an un- 
even land 
surface is de- 
pressed and 
partly covered by the sea, as in Fig. 228, ridges and hills 
stand forth as promontories and islands ; valleys are en- 
tered by arms of the sea ; protected harbors are plentiful 
in the earl}'- stages of shore lines of this class. 

The western coast of Norway is extremely irregular, hav- 
ing many small and large islands along its " outer shore line," 
while long arms of the sea, or fiords, carry deep water far 
inland between steep mountain walls. 

Sogne fiord, north of Bergen, penetrates the mainland 100 
miles, its branching arms giving assurance that it is a sub- 
merged valley. The depth of this and other Norwegian fiords 
is believed to have been increased by the scouring action of 
heavy ice streams from the highlands during the glacial period. 

The walls of the fiords are so steep that roads can seldom 
follow their shore lines; hence communication is chiefly by 
water. Settlements are found at the head of the fiords and 
on deltas built by inflowing streams. 

An irregular coast favors the development of maritime 
arts. Its outlying islands tempt exploration ; its protected 
bays afford safe harborage even for small boats. The 



SHORI] LINES. 



359 



people occupying the coastal lands become expert sailors 
and fishermen. 

The numerous bays of southern Scandinavia were known as 
viks to the people who occupied them 1000 years ago ; and 
the inhabitants were therefore called vik-ings, or bay people. 








: !!1:il|V'^ilV|^^;,,||l| 



Fig. 229. — A Delta in a Norwegian Fiord. 

They became bold marauders, invading and conquering the 
more southern coasts of western Europe, by whose people 
the vikings were called " Northmen." Normandy is to this 
day named after these early sea kings. They were the first 
European people to venture far out upon the ocean, and thus 
almost 1000 years ago they discovered Greenland and other 
parts of the western world. 

The west coast of Patagonia (southern Chile) resembles 
that of Norway. The Canoe Indians dwell here, — a primi- 
tive people who find the steep slopes of the land so inhos- 
pitable that they live almost entirely in open canoes on the 



360 PHYSICAL GEOGRAPHY. 

water. A small fire is kept burning on a few sods in the 
canoes, so that they may carry it from place to place. They 
have no fixed habitations and make little use of the land, 
except when they build temporary shelters of tree branches, 
roughly thatched, in one cove or another where they stop for 
a time to gather shellfish. 

Lake Shores frequently imitate the features of sea- 
shores of the second, class. When mountain valleys are 
warped, the lake waters rise on the mountain flanks and 
gain outlines of much regularity. Again, when lakes are 
formed back of barriers of glacial drift, their waters may 
rise upon an uneven land surface, transforming valleys 
into bays and hills into islands. 

Lake Lucerne, Switzerland, is an excellent example of an 
irregular lake in a warped mountain valley ; its many arms 
enter bays between bold promontories of great picturesqueness. 
The Lake of the Woods, on the northern border of Minnesota, 
overlaps the border of the rugged highland of Canada; its 
outline is extremely irregular, and numerous rocky hills rise 
as islands in the lake. The northern shore of Lake Superior 
is of exceptional beauty, its bold headlands and outlying 
islands separating many irregular bays, where the lake waters 
have risen upon an uneven land surface. 

Sea Cliffs and Benches. — The irregular seashore lines 
above described are relatively little changed from the 
outline produced by depression, except on the projecting 
headlands and the outlying islands. Here the sea may 
beat furiously, cutting a rocky bench beneath bold cliffs 
and sweeping away the waste of the cliffs into deeper 
water. Recesses are cut between outstanding ledges. 
Isolated rock columns or stacks stand up on the rock 
bench. 



SHORE LINES. 



361 



Angular rock fragments, weathered from a rocky coast, are 
swept about by the clashing waves, and are in time rounded to 
cobbles and pebbles. In storms the cobbles batter the rock 
face and grind the rock floor, thus cutting a notch in the 
edge of the land, forming a cliff that rises above sea level and 
a bench that may be partly bare at low tide. At high tide 
the waves roll across the bench and under-cut the base of the 
cliff. Great masses of rock fall from the cliff, and for a time 
protect its base ; but their shattered fragments are soon 
dragged off the bench by the waves and dropped into deeper 
water, and the attack on the cliff is then renewed. The force 
of storm waves on an exposed coast suffices to move great 
blocks of rock, 
even exceeding 
100 tons in weight. 
The Orkney and 
Shetland islands, 
north of Scotland, 
have lost much of 
their former area 
by the attack of the 
sea. Headlands 
break off in lofty 
cliffs, some of 
which are nearly 
1000 feet high. 
An isolated stack, 
known as the " Old 
Man of Hoy," rises 
600 feet above the 
sea. 




Fig. 230. — The "Old Man of Hoy.' 



Under the 
strong attack of 
the sea a steep coast may for a time be worn into a more 
irregular outline than its original form. 



362 



PHYSICAL GEOGRAPHY. 



The stormy promontory of western Prance, beaten by heavy 
waves and swept by strong tides, has thus gained a very ragged 
outline. The shore is dangerous from the many rocky reefs 
that rise to about half-tide height on the rock bench in front 
of the cliffs. Light houses on such reefs must be of the very 
strongest construction. 

Sea Caves. — If one part of an exposed sea cliff is 
weaker than the rest, the waves may excavate a cave in 
it, cutting away at the head of the cave faster than the 
overhanging roof weathers down. The length of such 
caves may reach 20, 50, or more feet. 

Fingal's cave, on the island of Staffa, west of Scotland, and 
many other less famous sea caves are of this origin. The 
" Ovens," on the coast of Mt. Desert, Maine, are shallow caves 
of similar natiire. 



Bay-Head Beaches. 



Storm waves sweeping into little 
bays or coves 
carry with 
them some of 
the waste that 
is washed from 
the benches of 
the enclosing 
headlands and 
from the shal- 
low bottom 

along shore. Beaches are thus formed around the bay 
heads (Fig. 231), and layers of sediment are strewn over 
the bay floor, while bare rock benches still front the head- 
land cliffs. 




Fig. 231. — Cliffs and Deltas on an Irregular Shore Line. 



SRORH LINES. 363 

Bay-head or cove beaches present a smooth curve, concave 
to the sea, on which the surf breaks evenly, quite unlike the 
dashing and fretting waves on ragged headlands. The cob- 
bles and pebbles thrown up on the beach during storms may 
form a wall 5 or 10 feet above high tide, back of which a pond 
or swamp is often enclosed in the valleys that previously 
opened into the bay. The New England coast has hundreds 
of small beaches of this kind between its rocky headlands. 

Sea Cliffs and Beaches. — As a sea cliff is cut back, 
the bench at its base becomes so broad that many cobbles 
and pebbles are not at once washed away into deeper 
water ; thus the beginning of a beach is made at the base 
of the cliff, and 
the rock floor 
of the bench is 
more or less 
concealed. 

The breadth 
which a bench 
must gain be- 
fore a beach 
forms upon it 
is greater on a coast exposed to strong waves than in more 
quiet water. In southwest Ireland, exposed to the violent 
winter storms of the North Atlantic, the ragged headlands 
have been cut back many hundred feet ; yet the benches have 
only patches of cobbles here and there, and are still for the 
most part without continuous beaches. 

With further retreat of the cliff the beach will be more 
continuously developed, and much of the material upon it 
will be washed along shore in one direction or the other. 




Fig. 232. — A Curved Shore Line. 



364 



PHYSICAL GEOGRAPHY. 



according to the movement of wind-driven waves and 
tidal currents. The ragged cliff is then worn to a more 
even front, as in Fig. 233, C 

The smoother the front of the cliff becomes, the more 
steadily maj- the tidal and wind-swept currents move along 
it, di'agging the pebbles and sand jostled by the waves. 




Fig. 233. — Diagram of a Retreating Shore Line. 

Instead of following around the curve of every bay, the 
currents swing across the little bays from headland to 
headland, building curved spits^ or harrier beaches, with 
the material brought from the cliffs. The bay heads are 
in time enclosed and deltas (JS, F, Fig. 233) grow in their 
quiet waters. The originally irregular shore line thus 
becomes more and more simplified. As the beached head- 
lands are cut back, the spits and barrier beaches retreat 
with them, and the coast gains a smoother outline; thus 
the development of the shore line approaches maturity. 



SHORi: LINES. 365 

The dangers of the headlands are somewhat lessened when 
their stacks and rocky reefs are worn away, and when the 
bench at the cliff base is covered with a somewhat yielding 
beach, instead of lying bare. At the same time the bays are 
more or less completely closed, and are therefore less adapted 
to seafaring settlements. 

Tide-Swept Bays. — Strong tides may hinder the for- 
mation of beaches across large bays, by preventing the 
movement of cross currents from headland to headland. 
The waste that is carried into such bays from the cliffs is 
ground to fine mud by the tidal currents, and forms exten- 
sive tidal flats about the bay head, bare at low tide. 

The Bay of Fimdy and the Bristol channel are not only 
kept open but are broadened by the action of the tides, which 
increase in strength towards the bay heads. The estuary of 
the Seine is open to the sea, in spite of the mature stage 
reached by the cliffs on each side. Vessels entering the 
estuary must keep to the channel between the mud flats, 
although at high tide a broad sheet of water is spread before 
them. 

A British steamer, some years ago, ran aground on these 
flats and was swung around square to the channel by the flood 
tide. When the tide began to fall, the ebb current scoured a 
hollow under the bow, and the vessel, unsupported bow and 
stern, broke in two amidships. The next flood tide scoured 
away the mud on which the middle of the broken hull had 
been siipported ; and thus within a day the vessel sank and 
was buried almost out of sight, a total loss. 

Land-Tied Islands. — An island is sometimes attached to 
the mainland by the backward growth of sand reefs that 
are supplied with waste from its cliffs. The fortified Rock 



366 



PHYSICAL GEOGRAPHY. 



of Gibraltar, belonging to Great Britain, was originally an 
island, but it is now tied to the mainland of Spain by a 

broad sand reef. Part of the 
reef is "neutral ground," occu- 
pied neither by Spain nor Great 
Britain. 



Effects of Depression and Eleva- 
tion. — When the further devel- 
opment of irregular shore lines 
is interrupted by depression, the 
work of cliff-cutting and bay- 
filling must be begun again, in 
much the same way as before. 

If a rugged land mass border- 
ing the sea is uplifted, its former 
cliffs and beaches may be found 
at a greater or less distance in- 
land from the new shore line. 
As time passes, the cliffs and 
beaches are weathered away and 




EuKopa Poinf 



Fig. 234. — Gibraltar. 

the abandoned shore line becomes indistinct. 

An elevated shore line, marked chiefly by rocky cliffs 
and benches with occasional beaches, may be traced along 
the greater part of the western coast of Scotland, at a 
height of 20 or 25 feet above sea level of to-day. The 
present shore line has, as a rule, reached a less advanced 
stage of development than that reached by the elevated 
shore line. 

This elevated shore line forms a convenient bench along 
which roads may be laid near the base of the slopes that 



SHORE LINES. 



367 



ascend to the highland summits. ' Villages and farmhouses are 
often situated on the broader benches. Sea caves, roughly 
walled in, sometimes serve as stables for the seaside farmers. 
Other elevated shore lines are found at greater altitudes. 




Fig. 235. — Easdale, a Village on an Elevated Shore Line, West Coast of Scotland. 

The sediments spread over the bay floors of a former 
shore line form, after elevation, local coastal plains between 
rugged headlands. Cliffs are again cut on the headlands, 
while smooth-curved beaches, sometimes many miles in 
length, front the little coastal plains (Fig. 236). 

Eegions of this kind are among the most bea,utiful parts of 
the world. Many examples are found along the coast of Italy, 
the Gulf of Salerno (next south of the, Gulf of Naples) being 
one of the most perfect. 'When viewed from one of the higher 
hills on the north, the bay sweeping to the headland on the 



368 PHYSICAL GEOGRAPHY. 

south and the plain sloping forward from the inner moun- 
tains, with the bright coloring of an Italian landscape, form a 
picture long to be remembered. 








Fig. 236. — Headlands and Bays. 

The withdrawal of lake waters by a change of climate 
(p. 318) has an effect on the condition of shore lines similar 
to that produced by an elevation of the land with respect to 
the sea. The cliffs and beaches that contour around the slopes 
of the mountains of Utah, where the waves of Lake Bonne- 
ville once beat, in many ways resemble the elevated shore lines 
of western Scotland. 

The western coast of Norwa}'^ is bordered for much of 
its length by a belt of low land, sometimes as much as from 
3 to 10 miles wide, from whose inner margin a bold ascent 
leads to the highlands (Fig. 237). The low land is a 
broad rock bench or platform, cut by the sea when the 
land stood about 300 feet lower than now. A large part 
of the population of western Norway dwells on this ancient 
sea floor. 

The former sea cliff, at the inner margin of the platform, is 
from 500 to 1000 feet high. A number of rocky hills surmount 
the platform, representing unconsumed islands of the former 



SHORE LINES. 



369 



time. The deep fiords of the highlands and many branching 
channels traverse the bench, so that its outer part is now fringed 
with islands. From this it is inferred that, after the cut- 
ting of the platform and cliff, the whole region was uplifted to 




Fig. 237. — The Coast Platform of Norway. 

a greater elevation than it now has ; and while in this position 
the valleys were eroded in the platform. Since then a depres- 
sion has occurred, drowning the valleys and thus converting 
the outer part of the plain into a swarm of islands, many of 
them so small as to be occupied only by a single family. 

The platform is wanting on certain parts of the Norwegian 
coast ; here the sea beats directly against the border of the 
highlands, as at Cape North, a great cliff 1000 feet high and 
nearly vertical. It is probable that at such points the land 
stands again in about the same position that it had while the 
platform was carved. Here the work of making the platform 
is still going on, and the shore line is becoming more and more 
mature. 

Delta Shore Lines. — Rivers tend to build their deltas 
forward, and thus oppose the destructive action of the sea. 



370 PHYSICAL GEOGRAPHY. 

The outline of a delta will therefore depend on the rela- 
tive strength of these opposing tendencies, whether on 
shore lines of the first or of the second class. 

A small stream entering an ocean of strong waves or 
tides can have little effect on the shore line. The action 
of the waves will cut back the land in face of the effort of 
such streams to build it forward. Tides of great range 
will not only prevent small streams from building deltas ; 
they may even widen the lower courses of the streams, 
forming estuaries. 

Streams that enter quiet waters build deltas without 
interference from strong waves and currents. A small 
river of a coastal plain, entering a lagoon back of a sand 
reef, builds a delta of convex front with projecting arms 
at the mouth of each distributary. 

A river of this kind may find no break in the sand reef 
opposite its mouth for the discharge of its waters into the sea. 
The nearest inlet may be many miles to one side of the river 
mouth. As the lagoon is filled by delta growth and tide 
marsh, the river maintains a channel to the inlet, thus making 
a square turn from its mainland course, and running for some 
distance parallel to the coast. 

Pedee river in South Carolina receives a branch from North 
Carolina whose waters flow southwest parallel to the coast at a 
little distance inland for 70 miles before reaching the point 
where a break in the shore ridges allows an escape to the sea. 
This seems to be a result of the process just described. 

A great river entering the sea where the strength of 
waves and tides is not excessive may build a delta which 
shows little effect of sea action. Examples may be found 
representing many stages between the extreme cases here 
indicated. 



SHORE LIKES. 



371 



The powerful Mississippi discharges a great quantity 
of land waste into the Gulf of Mexico. The waters of 
the gulf are relatively shallow and the tides are • weak. 
Here the outline of the delta seems to be governed en- 
tirely by the action of the great river {Fig. 191); 



The several distributaries of the Mississippi build low and 
slender banks of mud on each side of their channels ; hence 
the delta has several linger-like projections into the sea. In 
order to increase the depth of water in one of the channels, or 
"passes," jetties (dikes of wood and stone) have been built 
forward beyond the end of the delta fingers, thus increasing 
the current, and forcing it to scour the channel to a depth 
sufficient for seagoing vessels to enter. 

The Eio Grande, a large river, but much smaller than the 
Mississippi, delivers land waste to the gulf in greater quantity 
than the waves and currents 
can altogether remove ; hence 
its delta is built forward (Fig. 
238). But the waves are strong 
enough to smooth the outline 
of the delta ; hence it has a 
gently convex curve withoiat 
finger-like projections. The 
Brazos river, about midway 
between the Mississippi and 
the Eio Grande, also causes a 
slight forward bowing of the 
Texas coast ; here, as in the 
Rio Grande delta, the lagoon, 
that elsewhere lies behind the 
sand reef, is replaced by the 
delta deposits. It is probable 
that the Colorado river (of Texas) has aided the Brazos in 
building forward the coast line^ althoiigh it now enters a lagoon. 




Fig. 238. — Deltas of the Texas Coast. 



372 PHYSICAL GEOGRAPHY. 

Example for Review. — The coast of Maine is a worn- 
down old-mountain region. Like southern New England, 
the worn-down lowland has been uplifted and again dis- 
sected, many valleys being thus formed between ranges 
of hills. After the valleys were formed, a movement of 
depression (400-600 feet) converted many of them into 
bays reaching far inland. The land stood in this de- 
pressed position during the glacial period ; and while the 
ice sheet was melting away, much drift was washed from 
it into the long narrow bays. 

Since then a movement of elevation (about 300 feet) 
has laid bare the bay floors, where marine clays now form 
an irregular coastal plain enclosed by hills that were for- 
merly promontories and islands. The streams from the 
interior, flowing forward over the clay plains, have begun 
to dissect them, so that their surface is now uneven. The 
coast line is still very irregular, because the postglacial 
elevation was not so great as the previous depression. 

The farmed fields of southern Maine are very generally on 
the smoother parts of the clay plam. The rocky hills are 
wooded, except where covered with, enough drift to provide a 
soil worth cultivating. The peninsulas and islands are com- 
ing to be occupied as summer resorts by people from the 
interior states. 

Effect of Climate on Shore Lines. — Shore lines, like 
land forms, are affected by climate ; not only by differ- 
ences between regions of on-shore and off-shore winds, 
where waves and currents are stronger or weaker, but 
even more by differences of temperature. 

In polar seas the land is often bordered by a fringe of 



SHORE LINES. 



373 



ice called the ice foot. This is in part formed of fresh 
water that freezes on entering sea water whose tempera- 
ture is below 32°. During the winter the ice foot usu- 
ally remains attached to the land, unless broken by strong 
tides ; in summer it may melt, loosen, and float away. 

The ice foot is often used as a 'longshore roadway for 
sled travel by Eskimos and Arctic explorers. When loose 
from' the lands and moved on and off shore by the tides, 
stones are dragged beneath it, grinding the shore rocks round 
and smooth. 

In torrid seas, not exposed to strong surf, the shores 
may be invaded by certain kinds of trees, forming a net- 
work so dense as to make landing difficult. 

The mangrove is the most important tree of this kind. It 
grows freely in shallow sea water on low and muddy shores, 
and protects the land 
from the waves. Roots 
grow out from the 
trunk above water 
level. Crabs and oys- 
ters live on the stems 
and roots. Birds oc- 
cupy the branches. 
Muddy sediments ac- 
cumulate in the quiet 
water among the trees, 
and thus the land 
gains on the sea. 
Shores occupied by 
mangrove swamps are 

dismal as compared with the shell-strewn beaches of sand and 
pebbles, beaten by trade-wind surf. 




Fig. 239. — Mangrove Tree. 



374 PHYSICAL GEOGRAPHY. 

Coral Reefs. — The shallow waters of continental bor- 
ders or mid-ocean islands in the warmer seas are commonly 
occupied by coral reefs composed of the limy framework 
of coral animals. Living corals are found chiefly on the 
outer side of the reef where they grow in the shallow 
water much in the same way that a thicket of small bushes 
grows on the land. 

Eeef-building coral animals take the limestone needed for 
their skeletons from solution' in sea water. They are not 
found where the mean temperature of the water in the cool- 
est month is lower than 68° F., and they do not live at depths 
greater than about 20 fathoms. There are many different 
species, but all are fixed to the bottom. Some branch in 
bush-like forms 1 or 2 feet high (" stag-horn coral ") ; some 
grow in round masses from 1 to 3 feet in diameter ("brain 
coral"). 

The shores of a volcanic island in water of fitting tempera- 
ture might be colonized by corals, for the young forms float 
and are carried far and wide by ocean currents. The follow- 
ing succession of reef might then be produced. 

Fringing Reefs. — When reef-building corals first take 
possession of a new shore, their growth extends upward 
from the shallow bottom and outward into the surf, where 

the constant movement 
of the sea water supplies 
them, with food. When 
they are detached from 
the bottom by severe 

Fig. 240. — A Frmging Reef. i ti t i , 

storms and rolled about 
by the waves, the larger fragments of their limy framework 
are thrown back towards the land, forming shoals, and 




SHORE LIITES. 375 

sometimes rising in a beach a little above sea level ; the 
finer particles are carried off shore and strewn over the 
sloping bottom towards deep water. The reef thus broad- 
ens, forming a fringe close along the shore line. At this 
stage it is called a friyiging reef. 

Strips of fringing reef are found on the equatorial coast of 
east Africa, along parts of the Brazilian coast, at various points 
on the coast of Cuba and elsewhere in the West Indies, and 
bordering many islands in the Pacific, as the Hawaiian and 
other groups. The Galapagos islands in the eastern Pacific, 
close to the equator, are free from reefs, because of the low tem- 
perature of the water which there comes in a strong current 
from far southern latitudes, or which rises from below the sur- 
face along the Peruvian coast when the winds blow off shore. 

Fringing reefs are generally interrupted opposite the 
mouths of streams, where land waste makes the bottom 
muddy and unfit for coral growth. Water passages are often 
preserved back of the reef, close to the shore. Natural harbors 
are thus provided, well protected from the surf that breaks 
on the shoals and beaches of the outer reef. 

Barrier Reefs. — A fringing reef broadens by the out- 
ward growth of the corals, and the submarine slope is 
built forward by the sup- 
ply of coral fragments. 
At the same time water 
supplied by rain, by 
streams from the land, 
and especially by the 
surf that rolls over the reef, slowly dissolves and washes 
away the inner part of the reef where living corals are 
few or wanting. Thus the reef may come to be separated 




Fig. 241. — A Barrier Reef. 



376 



PHYSICAL GEOGRAPHY. 



from the land by a shallow lagoon a mile or more wide ; 
and in this way a fringing reef may change to a barrier reef. 




Fig. 242. — Part of the Great Barrier Reef of Australia (as seen at low tide, looking towards 
the mainland). 



The Great Barrier reef stretches along the northeast coast 
of Australia for about 1000 miles, the largest reef in the world. 
It is from 20 to 50 miles from the mainland, mostly beneath 



SHORE LINES. 



377 




Fig. 243. — Diagram of Part of a Barrier Reef. 



sea level, interrupted by numerous inlets, and bearing a few- 
low islets. The sea outside descends rapidly to great depths ; 
the water inside is shallow (from 10 to 40 fathoms). 

Effects of Elevation. — If a slow uplift occurs, corals 
will continue to grow 
on the outer face of 
the reef. At the same 
time, rainfall and surf- 
overflow may wear and 
dissolve away the up- 
lifted parts so tha,t the 
reef gains little height 
above sea level, and the lagoon is kept open beneath sea 
level. It therefore seems possible that barrier reefs may 
occur in regions of very slow elevation. 

If a relatively rapid uplift occurs, a reef may be raised 
above sea level, forming a terrace-like bench above the 
new shore line. Ele- 
vated reefs are known 
along many coasts in 
the torrid zone. 

An uplifted reef forms 
a bench at a height of 
about 30 feet, with a 
breadth of a mile or less, 
bordering much of the northern coast of Cuba. Corals are 
easily recognized in the ragged structure of the reef. It is 
seldom interrupted, except where rivers cut their valleys 
through it. The sea has worn a low cliff in the front of 
the bench ; from the cliff top one may look down upon the 
modern fringing reef now growing in the sea. 



M 


^W 


'^X 


h^' 


®^^^r^~~~~i 


1 


...A .. .. 




mi ! 


M^ 



244. — Diagram of Part of an Elevated Reef. 



378 



PHYSICAL GEOGRAPHY. 



Elevated reefs are relatively weak and cavernous struc- 
tures ; they may be worn down much more rapidly than 
the strong foundation rocks on which they are often 
based. In this way an elevated reef may be converted 
into a barrier reef again, the lagoon being dissolved out, 
while new coral growth takes place on the outer margin. 
Barrier reefs of this kind may be recognized as long as the 

island remnants of the 
elevated reef are not 
entirely worn away. 

Elevated reefs in vari- 
ous stages of destruction 
occur on the Fiji islands 
up to heights of 800 feet. 
Many of the barrier reefs 
of this group seem to have 
grown on the outer edge of platforms formed by the almost 
complete wearing away of elevated reefs, much of whose 
surface is now worn and 
dissolved away even a lit- 
tle beloMf sea level. 



Effects of Depression. 
— If a reef is depressed 
faster than corals can 
grow upward, the depth 
of water above it will 




Fig. 245. — Diagram of Part of a Denuded Keef enclosed 
by a Barrier Reef. 




Fig. 246. — Diagram of Part of a Drowned Keef. 



increase to a greater measure than that in which reef- 
building corals can live. Then the polyps are " drowned " 
and the reef is " dead." 



The Chagos Bank, in the Indian ocean, 1000 miles south 
of India, is a broad shoal measuring about 100 by 75 miles, 



SHORE LTNES. 



379 



at a depth of 40 or 50 fathoms. It is bordered by a ridge 5 or 
10 miles v/ide and 15 fathoms deep, on which a rim about 1 
mile wide rises to within 5 or 10 fathoms of the surface, bear- 
ing a few low islets here and there with some living coral. 
The banks appear to have once been an extensive coral reef, 
now drowned. 

The Marquesas islands in the eastern Pacific are a group 
of dissected volcanoes of irregular outline and steep slopes, 
with deep water close to shore, as if recently depressed. 
Cliffs are already cut in the headlands, and the bays contain 
beaches strewn with cobbles, among which coral fragments 
occur. There are no living reefs around the shores, although 
the temperature of the water is fitting and reefs abound in 
islands to the southward. It is probable that while the Mar- 
quesas stood higher, reefs were formed around them, and from 
these the coral cobbles of the present beaches have most likely 
been derived ; but the depression by which the present outline 
of the islands was determined appears to have been too rapid to 
permit the upward growth of the reefs to keep pace with it. 

Atolls. — If a slow depression takes place, it may be 
counteracted by the upward growth of the reef corals. 
Then the reef will be 
preserved ; it may even 




Fig. 247. — A Large Atoll. 



increase in size by out- 
ward growth during de- 
pression, as in Fig. 247. 
At the same time, the 
lower slopes of the island around which the reef first 
fringed will be drowned and its valleys will be occupied 
by bays ; if depression continues, the central island may 
altogether disappear, leaving only the encircling reef of 
oval or irregular outline around the lagoon. Such reefs 
are called atolls. 



380 PHYSICAL GEOGRAPHY. 

If a volcanic island witliin a barrier reef does not suffer 
uplift or depression, it must be slowly worn down closer and 
closer to sea level, while its barrier reef is growing outward. 
But it is doubtful whether the resistant rocks of such an island 
could be worn away below sea level, so as not to appear in a 
lagoon whose depth may be from 20 to 50 fathoms. For this 
reason the theory proposed by Darwin, that atolls result from 
the slow depression of islands with fringing or barrier reefs, 
has had general acceptance. 

Life on Atolls. — As coral islands are limited to the 
warm and uniform climate of the oceans in low latitudes, 
mostly within the torrid zone, they are bordered with 




Fig. 248. — An Atoll, or Coral Island. 



waters teeming with marine life, and many of. them bear 
a luxuriant vegetation. The natives of the larger atolls 
lead easy and indolent lives, but their progress towards 
better conditions than those of savagery is hindered by 
the small variety in their surroundings and by their dis- 
tance from lands of more varied form and products. 



SEORE LINES. 381 

Although, one of the most wonderful objects in nature, 
a lonesome atoll affords little opportunity for human 
development. 

The small height of atolls subjects them to the danger of 
being overwhelmed by earthquake waves. Hurricanes some- 
times come upon them unobstructed from the open sea, sweep- 
ing violent surf far up the beaches ; the storm winds break 
down the cocoanut palms on which the natives dej)end largely 
for food and for the materials, of many of their simple arts. 
There are no streams, but fresh water supplied by rains 
may be found a little below the surface. The thin soil has 
little variety of mineral matter, but floating pumice is often 
cast ashore from distant volcanic eruptions, and some of the 
islanders have learned to gather and pulverize it to use as 
a fertilizer for their little fields. Floating logs sometimes 
drift upon the islands, and their roots occasionally carry 
stones of firmer texture than coral rock (for example, frag- 
ments of dense lava from a volcanic island) ; whetstones, 
pestles, and mortars are made from these chance supplies. 

Although birds are plentiful, there wefe no mammals on 
coral-islands until rats and mice came ashore from vessels; a 
few domestic quadrupeds have occasionally been imported by 
foreign residents. 

Until the nineteenth century the natives of most of the 
Pacific islands knew nothing of the rest of the world. Their 
highest art was seen in the making of sail canoes, in which 
they voyaged between the islands of their archipelagoes. It 
was probably when blown from an intended course in these 
small boats that the islands were originally peopled from 
larger lands. 

The Tuamotu or Low archipelago in the eastern Tacific 
contains 80 islands, only 4 of which rise more than 12 feet 
above sea level. Most of the islands are atolls. The narrow, 
irregular reefs are partly below, partly above, tide level, but 
only ^\ of their land area is habitable. The islands are gen- 



382 ■ PHYSICAL GEOGRAPHY. 

erally higher on the windward (east and southeast) side, where 
wind and wave supply coral sand to make beach ridges. On 
the leeward side the surf is not so strong, and here many 
channels are kept open by outflowing currents. 

Like fringing and barrier reefs, atolls may be elevated. 
After elevation they may be worn down and again con- 
verted into atolls of the usual form without any central 
island. 

Metia, one of the Tuamotu group, seems to be an elevated 
atoll, with cliffs cut on the windward side. It measures about 
4 by 2^ miles, with a height of 250 feet. It consists entirely 




Fig. 249. — Metla, an Elevated Coral Island. 

of limestone, containing fragments of coral here and there, but 
generally of fine texture, as if composed of the coral sand and 
mud that formed the deeper parts of the former atoll. Many 
caverns are found in the limestone. 

Some of the atolls in the Fiji group are best accounted for 
by the denudation of elevated reefs, remnants of which are 
still to be seen standing somewhat above the general level. 
In these islands the corals that now fringe the atoll have had 
little influence on the form of the reef ; they only form a crust 
upon the platform of the denuded elevated reef. 

If the depression of an atoll is at such a rate that not 
enough coral waste is supplied to build the submarine 



SHORE LINES. 



383 



slope that descends into deep water, the outer margin of 
the reef may be slowly worn away, and thus the atoll will 
decrease in size. It 
may in time disappear 
entirely. 




Fig. 250. — A Smaii Atoll. 



Honden island, in the 
Tuamotu group, is about 
3 miles in diameter, wit 
a small central lagoon. 
The reef rises 12 feet above sea level, and is occupied by a 
belt of large forest trees. When visited by 'explorers, about 
1840, the island was 'tenanted only by birds, so tame that 
they were taken from the trees as if they had been their 
flowers. 

Jarvis island is close to the equator in longitude 160° W. 
It is about a mile in diameter. Its sandy surface is a little 
depressed at the center, but does not hold a lagoon. This is 
one of the smallest known coral islands. 



APPEIsrDIXES. 



APPENDIX A. 



Problem of Eudoxus (p. 11). — Eudoxus was one of the 

earliest of the Greek philosophers to demonstrate that the 
earth is not flat. His argument may be outlined as follows : 
Let NABCS be a part of a meridian line ; the lines DAE, 
FBG, and ^CJ" representing the horizons of observers at the 
points A, B, and C. Each observer can see only those parts 
of the sky that stand above his horizon. If the observer at 
B travel to C, he 



will lose sight of 
the stars X (sup- 
posed to be at a 
great distance away 
in the direction of 
the arrows), while 
the stars -^ will come 
into sight beneath 
the stars Y that he saw before. Eudoxus was in some such 
way as this led to argue that as he went north or south, his 
horizon plane tilted one way or the other, and hence that the 
surface of the earth must be convex. We may imagine that 
he "said : " Observations of this kind might be made by any 
one who travels north or south. On whatever meridian the 
observations are made, the result is the same. All meridians 
seem to have the same curvature, as if they were all circles 
of the same size. Hence the earth must be a sphere." 




Fig. 251. — Globular Form of Earth shown by Visibility of Stars. 



386 



PHYSICAL GEOGRAPHY. 



APPENDIX B. 



Problem of Eratosthenes (p. 12). — Eratosthenes was the 
first to measure the size of the earth. His method may be 
easily imitated as follows : A hill having north and south 
slopes, AD and AB (Fig. 252), may be taken to represent 
part of a small earth, FBADG. Set up two boxes, with ver- 
tical sticks nailed 
to their sides, at the 
points B and D, on 
a north and south 
line ; measure the 
distance BAD over 
the curve of the hill. 
(If no hill is avail- 
able for this experi- 
ment, set up two 
boxes on the north 
and south sides of a 
school yard, tilting 
each box slightly away from the other, as in Fig. 253, and 
representing the curve of the imagined earth by a series of 
stakes set up between the boxes.) 

The vertical sticks BJ and DK may then be regarded as 
extensions of the local radii 
OB and OD of the imagined 
earth FBADG. At midday, 
when the sun passes the me- 
ridian, the parallel rays of 
sunshine S'M and S"N fall 
in the same plane with the 
radii OB and OD. Measure the shadows cast at midday 
by the sticks J and K on the upper surface of the boxes. 




Fig. 252. — Sun Altitudes on the Two Slopes of a Hill. 




Fig. 253. — Sun Altitudes measured in a School Yard. 



APPENDIXES. 387 

Knowing the length of each stick above the box surface, the 
angles OJM and OKN may be determined. The angle 
BOD or J OK equals the difference between OJM and 
OKN. (JOK = JMK - OJM. But as &'M and &^N are 
parallel, JMK = OKN ; hence JOK = OKN - OJM.) Then 
we have the proportion : 

Angle JOK : 360° = distance BAD : circumference. 

Eratosthenes learned that at Syene (the modern Assouan) 
on the Nile, vertical objects cast no shadow at noon on June 
21. On the same day at Alexandria, about 5000 stadia north 
of Syene, he measured the angle between the sun's noon ray 
and a vertical rod, and found it to be 7^°. As the earth- 
radius at Syene lay in a line with the sun's ray, while the 
radius at Alexandria made an angle of 7-^° with the sun's ray, 
he saw that the angle between these radii at the earth's cen- 
ter must be 7^°. He then made the proportion : 

7^° : 360° = 5000 stadia : circumference of the earth. 

There is some uncertainty as to the accuracy of the meas- 
ure made by Eratosthenes, because the length of the stadium 
is not accurately known in terms of modern units of distance ; 
but as the distance between Syene and Alexandria is about 
500 miles, his result could not have been far from the truth. 

The problem of Eratosthenes may be repeated in essence by 
the students of two schools at places about north and south 
of each other ; for example, at Cleveland and Savannah, or at 
Chicago and Mobile. At noon upon a certain day, agreed 
upon by correspondence, determine the angle between a ver- 
tical rod and the sun's rays at each place. Measure the dis- 
tance between the two places (better, the meridian distance 
between their parallels of latitude) on a good map. Then 
take the difference between the two angles and repeat the 
above proportion, 



388 PHYSICAL GEOGRAPHY, 



APPENDIX C. 



Latitude and Longitude (p. 17). — On tlie supposition 
that tlie eartli is splierical, the arc of a meridian from a 
given point to the equator measures the latitude of that 
point. Tlie arc of the equator between two meridians meas- 
ures the difference of longitude between all places on those 
meridians. 

The terms latitude and longitude, or " breadth " and 
"length," were introduced in ancient times with reference 
to the countries around the Mediterranean Sea, where the 
dimensions of the known lands were greater east and west 
than north and south. As exploration proceeded, the same 
terms were extended all over the globe, although no longer 
appropriate in their meaning. 

Latitude. The latitude of a place may be roughly deter- 
mined as follows : 

In consequence of the rotation of the earth, the sun and 
stars seem to move around us in circles. The circles thus 
traced in the sky are arranged like parallels of latitude on 
the earth ; they are all parallel to one another and have the 
north and south poles of the sky in common. 

A few hours' observation on a clear night will aid in 
understanding the apparent motion of the stars. Several 
rods may be used as ''pointers." Set a rod so that it points 
to a star. After an hour or two, compare the direction of 
the star with that which it had before, as indicated by the 
pointer. If observations of this kind are made on various 
stars in different parts of the sky, it will be found that over 
the northern horizon the stars move in arcs of relatively 
small circles about the sky pole. About 90° away from 
the pole, and therefore near the equator, the stars move 
much more rapidly in arcs gf larger circles. By leaving the 



APPENDIXES. 389 

pointers unmoved till the next evening aucl beginning obser- 
vations a little earlier than before, the stars may be seen to 
approach and pass their previous positions. Hence each star 
makes a whole circuit in a day (strictly, in 23 h. 56 min.). 
The path of the sun should be traced in the same way. 

Observers in temperate latitudes may see a good number of 
stars in the neighborhood of the sky pole that do not sink 
below the horizon in their daily circuits ; these are called 
circumpolar stars. 

For an observer at the pole, the horizon would stand par- 
allel to the star circles. As the observer moves towards the 
equator, his horizon is more and more inclined from its posi- 
tion at the poles, and makes a larger and larger angle with 
the star circles. At the equator, the horizon and the star 
circles are at right angles to each other. The angle formed 
by the plane of the horizon with that of any star circle is, 
therefore, the measure of the arc of the meridian from the 
pole to the observer. The difference between this arc and 
90° is the local latitude. Any student who is familiar with 
the apparent movement of the stars across the sky may 
thus roughly estimate his position with respect to pole and 
equator. 

In consequence of the annual motion of the earth around 
the sun, the (apparent) diurnal motion of the sun is not 
strictly in a circle parallel to the star circles, but is in a 
slightly oblique line ; the sun thus moves north and south in 
the sky in the course of a year. But in a single day the sun's 
path does not depart significantly from a star circle. As the 
sun may be observed much more conveniently than a star, 
it may be used for a first rough determination of latitude, in 
the following manner : 

Drive a peg into the ground and to its top attach a pointer 
that may be easily turned to any part of the sky. At an 
early morning hour direct the pointer towards the sun (it 



390 



PHYSICAL GEOGRAPHY. 



will be properly set when turned so that it casts a shadow 
no larger than its cross section on a paper held behind it), 
and record the position of its end by driving a stake into 
the ground so that the top of the stake shall just touch the 
end of the pointer. 

Repeat this process several times during the day. The 
tops of the stakes will then mark part of a circle whose 
plane is parallel to that followed by the sun. Standing at a 
little distance to one side, the stake-toj) circle may be seen 
edgewise, so as to appear as a slanting straight line, AD. 

The angle I) AC that this 
line makes with the hori- 
zon measures the arc of 
the meridian from the ob- 
server to the pole. The 
angle DAU that it makes 
with a vertical line meas- 
ures the latitude, as ordi- 
narily counted from the 
equator. The advantage 
of this method is that it can be performed without knowing 
the position of the sun with respect to the sky equator. 

The latitude of a place is also measured by the altitude of 
the pole of the sky. (Atmospheric refraction is not consid- 
ered in any of these problems.) At the equator the sky pole 
would lie on the horizon ; and for every degree of latitude 
that the observer moves north, his horizon would dip a 
degree below the sky pole. The North star is about a degree 
and a half from the north pole of the sky ; but, in rough 
measures, the altitude of the North star may be taken as 
equal to the latitude. 

Latitude may be determined by measuring the noon alti- 
tude, or meridian altitude, of the sun, provided the angular 
distance of the sun from the sky equator is known. The 




.,.M„.,,j-^^. .;■ 
Fig. 254. — Sun-Circle Method of Measuring Latitude. 



APPENDIXES. 



391 



meridian altitude of the sun is SAC (Fig. 255). If its angu- 
lar distance from the sky equator is SAD, then SAC — SAD 
-— DA C = the meridian altitude of the sky equator = 90° 
minus the local latitude. This method is commonly employed 
for determining the latitude at sea, the sun's position with 
respect to the equator being given in the Nautical Almanac. 

On a spherical earth latitude might be defined as the angle 
in a meridian plane, limited by the radii drawn to the equator 
and to the place of observation. But on the spheroidal earth 
latitude must be defined, not by the angle between the radii, 
but between the verticals AM and QM, or between the hori- 
zon planes AB and QB, for CBQ = AMQ. Latitude may 




Pig. 265. — Latitude on a Spheroidal Earth. 



then be defined as the angle between the tangents to a 
meridian at the place of observation and at the equator. 

Longitude. There is no meridian from which longitude 
may be counted as naturally as latitude is counted from the 
equator; but it is customary in English-speaking countries to 
take the meridian of the astronomical observatory at Green- 
wich on the Thames below London as the prime meridian. 
Difference of longitude may be determined as follows : 

Imagine two observers on different meridians. Let each 
observer set his clock to noon, when the sun passes the plane 



392 PHYSICAL GEOGRAPHY. 

of his meridian. (This moment may be determined by noting 
the time when a vertical rod casts the shortest shadow on 
a horizontal surface.) If the two observers could then com- 
pare their clocks, the difference of the two local tiiaes would 
give them their difference of longitude, reckoned in hours 
and minutes (24 h. = 360°). The comparison of times may 
be made when a lunar eclipse happens, as follows : 

The eclipse being caused by the entrance of the moon into 
the earth's shadow, it must be seen at the same moment by 
all observers. Hence, if two observers note the local time of 
the beginning of a lunar eclipse and then by correspondence 
compare their records, the difference of the local times gives 
their difference of longitude. This method was first employed 
by Strabo, about the beginning of the Christian era. The 
date of eclipses may be found in almanacs. 

Another method involves the carrying of a timepiece 
from one place to the other. Let the students in two 
schools, as in Cincinnati and St. Louis, set their watches to 
noon at the passage of the sun across their local meridians. 
Then let either school send a watch by express to the other 
school. A comparison of local times can then be made. The 
result can be confirmed when the watch is returned. This 
method has frequently been employed in determining the dif- 
ference of longitude between the capitals of various coun- 
tries, a number of very accurate timepieces (chronometers) 
being carefully carried from one place to the other. 

Longitude is determined at sea by a similar method, A 
chronometer set to Greenwich (or some other) local time is 
carried on the vessel. Local noon is determined by noting 
the time when the sun rises highest above the horizon in its 
daily circuit. After certain corrections are made the differ- 
ence between Greenwich and local time gives the longitude. 

A very simple method may be employed for finding the 
difference of longitude between two places that are connected 



APPENDIXES. 393 

by telegraph. Let the local time be ascertained, as described 
above, at each place. At some day and hour agreed upon, let 
the observers at each place go to their respective telegraph 
offices and exchange time signals ; that is, at certain even five 
seconds, as indicated by the watch, let the observer at one 
place send a telegraphic signal to the other observer, who 
records the time of its arrival. Local times may be thus 
comj^ared with great accuracy. This method has now been 
employed not only between neighboring cities, but across the 
whole breadth of the United States, and by cable across the 
Atlantic. It may be easily repeated between schools a hun- 
dred or more miles apart, at a very moderate cost. 



APPENDIX D. 

Globes, Maps, and Models (p. 17). — In the study of geog- 
raphy it is necessary to represent the earth, or parts of 
it, in a form convenient for study. This is done on globes, 
maps, and models. Globes are excellent in showing the gen- 
eral distribution of land and water over the whole earth, 
with true outlines and correct relative positions ; but they 
cannot be made large enough to exhibit the small features of 
land forms.'- 

Maps necessarily have some distortion, for it is impossible, 
without crowding or stretching certain parts, to represent the 
convex surface of the earth, curved east and west as well as 
north and south, on a plane surface. But maps of parts of the 
earth have the advantage of being easily constructed of a size 
large enough to exhibit even the smaller features of the lands. 

Models are less cominonly used than globes or maps, but if 
well constructed they are of great value, as they may repre- 
sent the form of the lands over moderate areas with great 

1 An inexpensive &ix-incli globe is made by A. Donnelly, O^f nxl, N. Y. 



394 



PHYSICAL GEOGRAPHY. 



fidelity. Views of the Harvard Geographical Models, de- 
signed by the author, are given in Figs. 71, 72, and 122.^ 
Models are sometimes made with the sea surface convex, like 
that of the earth ; they then correspond to parts of large 
globes. A model of the United States, on a true-curved 
surface, is reproduced in Plate A, to illustrate the physical 
features of the country.^ It is important that the height of 
ridges and mountains on models should not be much magni- 
fied in proportion to their horizontal measures. 

Projection of Maps. In the construction of maps, the 

meridians and parallels are first 
drawn as guide lines by a method 
called projection (see below) ; then 
the outlines of land and water, 
the position of boundaries, cities, 
etc., are drawn in according to 
their determined latitude and lon- 
gitude, or according to their dis- 
tance and direction from known 
points. 

In order to present half of the 
earth's surface, the StereograpMc 
projection is commonly employed 
as follows : 

Let the map plane touch a 
globe at the equator, as in Fig. 
256. From the opposite point on 
the equator imagine straight lines drawn through various 
points on the meridians and parallels ; prolong or project 
these lines till they intersect the map plane. The projected 
position of the guide lines is thus determined. The central 

1 These models are published by Ginn & Company. 

2 This model is made by E. E. Howell, 612 17th Street, N. W., Wash- 
ington, D. C. 




Fig. 256.— The Stereographic Projection. 



APPENDIXES. 



395 



part of sucli a map is in true proportion ; at the margin 
distances are doubled. In actual practice projection does 
not require the aid of a globe ; the position of tlie projected 
guide lines is constructed by an ingenious use of geometry on 
the map plane itself. 

When it is desired to represent nearly all the earth on 
a single map, the Mercator j>rojectio7i is commonly used as 
follows : 

Imagine a cylinder touching a globe around the equator, as 





Fig. 257. — The Mercator Projection. 



Fig. 258. —The Conical Projection. 



in Fig. 257. From the center of the globe project the guide 
lines upon the cylind-er. Cut the cylinder down one side, and 
open it flat. The equator and parallels are then horizontal 
lines ; the meridians are vertical lines. There is no distortion 
around the equator, but there is an increasing exaggeration 
towards the poles ; hence the polar regions are not represented 
on maps of this kind. 

When a small part of the earth's surface, such as Germany 
or Mexico, is to be mapped, the Conical jjrojection (or some 
modification of it) involves relatively little distortion. Imag- 
ine a cone touching the earth on a latitude circle that passes 
through the middle of the country to be mapped. Project 



396 



PHYSICAL GEOGRAPHY. 



lines from the center of the globe to the enclosing cone. 
When the cone is split and unwrapped, the meridians are 
divergent straight lines, and the parallels are concentric 
circles. 

Many other methods of projection are also employed. 




Fig. 259. — Representation of Relief by Hachures. 



Relief. The unevenness of a land surface is technically 
known as relief. Models have the advantage of showing 
actual relief. On maps relief is shown in various ways. 
Hachures are lines drawn in the direction of the surface 
slope, — longer and finer for gentler slopes, shorter and darker 
for steeper slopes. Hachures are used on the maps of the 
U. S. Coast and Geodetic Survey (generally known as the 



APPENDIXES. 397 

'^ Coast Survey"). Contour lines, or contours, represent level 
lines along the side of a slope, as if marking the shore lines 
of the ocean at successive stages of its rise on the land. 
They are placed so as to be separated by definite vertical 
intervals, such as 50 or 100 feet ; consequently they stand far 
apart on gentle slopes and close together on steep slopes. 
Contours are used on the maps of the U. S. Geological 
Survey, and should become familiar by frequent use. Exam- 
ples of contour maps are given in Figs. 134, 137, and 153. 

Lists and prices of tlie maps published by these surveys may 
be obtained without charge on addressing the Superintendent 
of the U. S. Coast Survey, and the Director of the U. S. 
Geological Survey, Washington, D. C. Many of the maps 
are of great value as geographical illustrations. A general 
account of many of them is given in "Governmental Maps 
for use in Schools," Holt & Co., New York. The maps 
published by the Geological Survey can be had for two cents 
apiece when bought by the hundred. 

Relief is sometimes indicated by shading, so that one side 
of a hill or mountain appears lighter than the other side. 
Darker tints are sometimes used to indicate greater heights. 
Good examples of both these methods have been prepared 
for the state of New Jersey; they may be bought at moderate 
price from the State Geological Survey, Trenton, N. J. 

Scale of Maps. The ratio of a distance on a globe or map 
to the same distance on the earth is expressed by the scale. 
A globe 8 inches in diameter is on a scale of about 1 inch to 
1000 miles. Many maps are on a scale of about 1 inch to 50 
or 100 miles. The scale may be expressed by a fraction — a 
scale of 1 inch to 2 miles being x2^V2o ^^ nature. The sim- 
pler fraction, X25V00' ^^ adopted for many of our national 
maps. A scale of ^2^00 corresponds closely to that of an 
inch to a mile. 



398 PHYSICAL GEOGRAPHY. 



APPENDIX E. 

Terrestrial Magnetism. — The earth acts as if it were a 
great magnet ; this being one of its most remarkable and use- 
ful properties. In response to the earth's magnetism, a mag- 
netic needle, delicately suspended on a vertical pivot, will 
take a definite direction, about north and south in many 
parts of the world. The magnetic needle or compass thus 
■ serves as a guide on pathless lands and seas. 

As the needle seldom points true north, its departure from 
the meridian must be determined. This angle is called the 
Tnagnetic variation or declination. It may be found by com- 
paring the direction of the needle with the shadow of a 
vertical rod at midday. The variation slowly changes from 
year to year. 

The compass was invented by the Chinese. It was intro- 
duced into Europe about 800 years ago. When Columbus 
made his first voyage, the magnetic variation in Europe was 
west of true north. He found that it decreased as he sailed 
westward, and soon after passing the longitude of the Azores 
he discovered a point where the variation was zero. Farther 
west the variation was found to be east of true north, increas- 
ing as he sailed west from the point of no variation. 

A few years later, when Spain and Portugal were in dis- 
pute about lands then newly discovered, it was decided by 
the Pope that Portugal should have the lands to the east of 
the meridian that ran through the point of no variation, and 
Spain all the lands to the west of it. The eastern point of 
South America lay east of the dividing line, and hence fell to 
the share of Portugal, which thus gained possession of Brazil. 
For that reason Portuguese is spoken there to this day, while 
Spanish is the language of the other American republics from 
Mexico southward. 



APPENDIXES. 



399 



Since the time of Columbus it lias been found that the line 
of no variation (connecting all points where the needle points 
due north) is not a meridian, and that it shifts its position. 
About 1500 it lay on the mid- Atlantic. About 1600 it ran 
from Finland to Egypt. In 1700 it again traversed the 
mid-Atlantic. Now it runs through the United States from 
lower Michigan to South Carolina. At all places in the 
United States east 
of the line, the com- 
pass needle points 
to the west of the 
true meridian ; at 
all places west of 
the line, to the 
east. 

If lines of mag- 
netic north (often 
called " magnetic 
meridians ") are 
drawn through 
many places and 
prolonged, always 

following the guide of the needle, tLey will converge and 
meet at a point called the north magnetic pole, in the north- 
ern part of the Canadian province of Keewatin (northwest 
of Hudson Bay, latitude 70°). If the magnetic meridians are 
prolonged southward, they converge towards a south magnetic 
pole, far south of Australia. On the (true) polar side of the 
magnetic poles the variation of the compass may be 180° ; its 
north end would there point south. 

When the values of magnetic variation are found for many 
places and entered on a map, lines may be drawn through 
the places where the values are alike. These are called 
"lines of equal variation," as in Fig. 260. 




Fig. 260. — Lines of Equal Magnetic Variation. 



400 PHYSICAL GEOGRAPHY. 



APPENDIX F. 

The Annual Movement of the Earth around the Sun and 
its Consequences (pp. 27 and 35) may be best explained after 
pupils have been led to notice the stars seen in the east 
shortly after sunset. Observations made once a week or 
fortnight suffice for this purpose. If they are patiently con- 
tinued, it may easily be shown that a line from the sun 
through the earth points successively to different groups of 
stars ; but that at the end of a year it points again to the 
group with which the observations began. Recognizing that 
the stars are very far away, much farther than the earth is 
from the sun, the movement of the earth around the sun once 
in about 365 days can be thus reasonably proved. An under- 
standing of the earth's revolution thus gained is of much 
greater value than the memory of a text-book paragraph. 

The following construction will be found to give a better 
explanation of the cause of the seasons, as dependent on 
the inclination of the earth's axis, than can be gained from a 
ready-made diagram. 

Through the middle of a sheet of paper that measures 10 
or 20 inches on a side, draw a straight line parallel to one 
side. Let this middle line represent 200 arbitrary units of 
length. Mark two points, one on each side of the middle 
of the line, so that they shall be 3 units apart. Drive two 
pins through the paper at these points so that they shall 
stand firm. Place a loop of thread, whose perimeter meas- 
ures 189 units, over the pins ; stretch the loop tight with a 
pencil ; and thus guided draw a curve around the pins. It 
will look like a circle, but it is an ellipse, and represents the 
true form of the earth's orbit. Take out the pins, and around 
one pin hole draw a circle a little less than 1 unit in diameter ; 
this represents the sun, the units being niillions of miles. 



APPENDIXES. 401 

The distances from the sun along the middle line of the paper 
to the orbit will be 91|- and 94|- million miles. The earth 
occupies the first of these points (called ])^^'^helion) on Janu- 
ary 1, and is then nearer the sun than at aiiy other time of 
the year. The opposite point {aplielioii) is occupied on July 1. 
On this scale the earth would be a minute dot, hardly visible. 
It must be magnified to a globe (wooden ball) about one inch 
in diameter, and set up on a small flat support with a pin or 
wire for its axis. The ISTorth star being supposed to lie on 
the upper side of the paper, the earth must move around its 
orbit so that when seen from the sun it passes from right to 
left. Move the earth back from its position on January 1 by 
^ of a quadrant ; this is the position for December 21. In 
this position, tilt the upper end of the axis 23-^° away from 
the vertical and away from the sun. The earth is then set in 
its proper attitude. Now move it slowly around the orbit, 
always keeping the axis parallel to its oblique position on 
December 21. It will then clearly appear that the sun's rays 
will shine unequally on the northern and southern hemispheres 
in different parts of the orbit. The limits of the zones are 
easily defined. By turning the earth on its axis, it may be 
seen that a point, as in latitude 40° N., will have oblique 
(weak) sunshine and short days with long nights in the 
winter months, and steeper (stronger) sunshine, with longer 
days and shorter nights in the summer months. The times of 
shortest days and shortest nights are the solstices, December 
21 and June 21, respectively. At two points on the orbit 
(found by drawing a line through the sun at right angles to 
the solstitial line), the days and nights are equal ; these 
points are called the equinoxes, and are passed on March 20 
and September 22. The sun will be vertical at noon at 
some time during the year at every point within 23^° north 
or south of the equator — the zone thus defined being called 
the torrid zone. On December 21 the sun will not be seen 



402 PHYSICAL GEOGRAPHY. 

from any point within 23-|-° of the north pole ; on June 
21 it will not be seen from any point within a similar space 
aronnd the south pole — the spaces thus defined being called 
the north and south frigid zones. The north and south tem- 
perate zones lie between the torrid and frigid zones ; they 
never have a vertical sun, or a day in which sunlight does 
not reach every point within their limits. Frequent prac- 
tice with school-made apparatus will make the problems of 
the seasons and the zones well understood. 

APPENDIX G. 

The Circulation of the Atmosphere (p. 29). — The inter- 
esting problem of the atmospheric circulation as modified by 
the earth's rotation cannot be profitably taken up in a book 
of this grade. Attention should be given chiefly to the more 
important members of the circulation seen in the lower cur- 
rents or winds, as described in the text. It may be briefly 
stated that, on account of the earth's rotation, there is a force 
that tends to deflect all horizontal motions (whatever their 
direction) to the right in the northern hemisphere, and to the 
left in the southern. This force is zero at the equator, and 
strongest at the poles. The temperature being unlike at the 
equator and poles, gravity tends to produce interchanging 
currents along the meridians. The earth's rotation deflects 
these motions to the right or left, according to the hemi- 
sphere, and the resultant motions greatly affect the dis- 
tribution of pressure that would result from differences of 
temperature alone. Instead of finding high atmospheric pres- 
sure in the cold polar regions, the pressure there is lower 
than at the equator ; and a belt of high pressure is found 
about latitude 28° or 30° N. and S., this belt defining the 
" meteoi-ological tropics." See the author's ''Elementary 
Meteorology," 1894. 



APPENDIXES. 403 



APPENDIX H. 

Clouds and Rainfall (p. 31 and 45). — A greater amount of 
water vapor can be contained in warm than in cold air. When 
as much vapor is present as can be formed at a given tempera- 
ture, the air is said to be saturated. When air is not saturated, 
it may be made so by cooling it until the temperature falls to 
that degree at which the amount of vapor present is as much 
as can be contained. Any further cooling will make the air 
cloudy, and if continued far enough will cause rain or snow. 

The chief processes by which large masses of air are cooled 
sufficiently to become cloudy and yield rainfall are : (1) mix- 
ture with colder air masses ; (2) movement into a region 
where sunshine and radiation from the earth cannot maintain 
the preexisting temperature ; and (3) an ascending move- 
ment (generally very oblique), whereby the air rises and the 
pressure of the overlying atmosphere upon it is reduced, so 
that it expands and cools. The first of these processes occurs 
in the whirling winds of cyclonic storms, but it is probably 
of much less importance than the others. The second pro- 
cess takes place when winds move towards the pole, and espe- 
cially when this movement carries them from warm seas to 
cold lands, as in passing during the winter season from the 
Gulf of Mexico or the Atlantic towards the Great Lakes in 
front of a cyclonic center. The third is of great importance 
when winds encounter mountain ranges over which they 
must rise ; and again in cyclonic areas, where the whirling 
winds slowly ascend to great heights. 

It should be noted that the cooling of ascending currents 
is hardly influenced at all by the cold of lofty mountain tops, 
or by the low temperature of the upper atmosphere that they 
enter. The cooling is the immediate result of the expansion 
of the ascending air. Cooling of this kind may be felt in a 



404 PHYSICAL GEOGRAPHY. 

small way when the air is allowed to escape from its com- 
pressed condition in a bicycle tire by opening the valve. 

By reversing the above processes the conditions of clear 
and dry weather are indicated. The clouds of cool winds 
will be dissolved when the winds mix with warmer currents. 
Movement towards the equator, where higher temperatures 
are produced, will increase the capacity of air currents for 
vapor. They will then dry the surface over which they blow. 
It is in this way that the trade winds produce deserts. When 
air descends from aloft, it is compressed by the weight of the 
air that rolls in upon it above. It is thus warmed ; and if it 
contained any clouds at first, they will be speedily dissolved. 
Hence winds that become cloudy and give forth rain on one 
side of a mountain range will be clear and dry when they 
descend on the opposite slope. In the same way the air of 
anticyclonic areas is clear and dry, because it settles down 
from great heights to supply the outflowing winds at the 
base. 

The many forms assumed by clouds afford better material 
for observation than for definition. Students should be led 
to describe and to classify the ordinary cloud forms, and to 
note their prevalent direction of movement and their altitude 
relative to one another, rather than to learn names and 
descriptions from a book. The chief classes of cloud form 
are : the curmdus, or heaped cloud, of massive structure and 
moderate altitude, characteristic of daytime and fair weather ; 
the cirrus, or curled cloud, of delicate, fibrous structure and 
great altitude ; nimbus, or rainfall cloud, heavily covering the 
sky, and yielding rain or snow. Cumulus clouds are formed 
in local ascending currents of air ; they sometimes grow into 
the nimbus of thunder storms. Fibrous cirrus clouds may 
often be traced westward to a source in thin sheet-clouds, 
called cirro-stratus, and these in turn to a source in the heavy 
nimbus of a cyclonic area. 



APPENDIXES. 405 



APPENDIX I. 



Weather Observations and Weather Maps (p. 49). — A 
thermometer, barometer, wind vane, and rain gauge suffice 
for elementary observations of the weather. The more accu- 
rate the instruments are, the better, but useful results can be 
obtained with instruments of very moderate cost. Observa- 
tions should be conducted so as not only to determine the gen- 
eral change of tlie seasons, but also to exhibit the relation of 
local weather to the general phenomena exhibited on the 
United States weather maps. For this purpose it is desirable 
to give attention to one weather element at a time ; for exam- 
ple, first wind, then clouds and rainfall, next temperature, 
finally pressure. Each of these elements should be noted 
during the passage of one or two cyclonic and anticyclonic 
areas represented on the weather maps. After the several 
weather elements have been studied singly, they may be 
observed in their natural combination ; thus an understand- 
ing may be gained of the relation between local and general 
atmospheric conditions. Local and distant phenomena may be 
compared ; thus a period of settled fair weather illustrates the 
weather of the trade wind belt ; a period of changing weather, 
the weather of the north and south temperature zones. 

Accompanying these observations, exercises on the con- 
struction of weather maps may be given. Here, as in local 
observation, it is well to give attention to one element at a 
time, as in Pigs. 12 and 15. The correlation of the various 
weather elements in cyclonic and anticyclonic areas, the east- 
ward progress of these areas, and the resulting weather changes, 
should be discovered by the pupils themselves, as far as pos- 
sible, from the study of a selected series of typical weather 
maps. There are few subjects better adapted to the inculca- 
tion of scientific methods than the study of weather changes. 



406 



PHYSICAL GEOGRAPHY. 



Daily weather maps can be obtained from the nearest 
publishing station of the U. S. Weather Bureau at a nomi- 
nal cost. If publicly displayed where they may be of gen- 
eral service, they may usually be obtained free of charge. 
A collection of such maps is of great service in teaching ; 
the more striking examples of cyclonic and anticyclonic 
areas should be noted as types. Information regarding the 
distribution of the maps may be had on addressing the Chief 
of the Weather Bureau, Washington, D. C. 



APPENDIX J. 



The Moon and the Tides (p. 86). — Let C (Fig. 261) be the 
common center of gravity of the earth and the moon. Both 
bodies revolve around this center once a month (27|: days), 
the plane of the page being the plane of their revolution, and 




Fig. 261.— The Tidal Problem. 

AFBD being the earth's equator. The attraction exerted by 
the moon on a part of the earth at E is just equa,l to the 
resistance (centrifugal force) that this part offers to turning 
from a straight line, EJ, into its curved path, EG. At A the 
attraction of the moon is a little greater, and at-^ a little 
less, than at^. The resistances to curved motion (centrifugal 
force) are everywhere alike. Hence at A and B there must 
be small unbalanced forces, t^ and t^^, directed outward from 



APPENDIXES. 407 

the earth's center, and lying on the line ^M. As the earth 
turns on its axis, any point on the equator AFBD must be 
acted on by the forces t^ and t^^ every 12 hours 26 minxites. 
The forces are very weak, and the waves that they produce in 
the oceans must be very low ; but they are perceptible when 
increased by running on shore. 

The only point that may be obscure in this statement is 
the constant value of the resistance to curved motion at all 
parts of the earth. But remembering that the diurnal rota- 
tion of the earth may be overlooked while the tidal forces are 
discussed, it should be seen that the monthly movement of 
the earth around C must be accomplished witJiout angular 
turning, a given side of the earth always facing in a fixed 
direction. If this be tried experimentally with a disk of 
paper, or with a small globe, it will be seen that all parts 
of the earth thus moved will describe circles of the same size 
as that which carries E round C ; and that at any moment 
all parts are moving in the same direction ivith the same 
velocity. Hence all parts must have the same resistance to 
curved motion. If this important point is once grasped, 
there should be no further difficulty in the demonstration of 
the unbalanced forces at A and B. 

The value of the tidal forces t^ and t^^ may be roughly 
calculated in terms of gravity, as follows : 

As the moon's mass is -^l of the earth's mass, and as the 
distance from the moon to the earth is sixty times the 
earth's radius, it follows that lunar attraction at E is 

QA ' >rA\2 ' °^ 2¥Fooo of terrestrial gravity. Lunar attractions 

at A and B are (f §)^ and (f f)^ of lunar attraction at E. The 
excess of lunar attraction at A and the deficiency at B with 
respect to the value at E will measure the value of the small 
unbalanced forces to which the tides are due. These will be 
found to be about 0.0000001 of terrestrial gravity. 



408 PHYSICAL GEOGRAPHY. 

The Sun also causes tides in the oceans, but, in spite of 
the great size of the sun, its distance is so much greater than 
that of the moon that the solar tides have only about one- 
third of the strength of the lunar tides. Hence the lunar 
tides are not overcome, but only modified by the solar tides. 
At time of new and full moon, when lunar and solar tides fall 
together, the tidal range is increased, low tide being lower as 
well as high tide being higher than usual. Sprmgtide is the 
name given to this condition of strong range. At the first 
and third quarter of the moon, the solar forces attempt to 
make low tide where the lunar forces make high tide, and 
vice versa ; hence at such times the tidal range is decreased, 
low tide being not so low and high tide being not so high as 
usual. Neaptide is the name given to this condition of weak 
range. It is often the case that the range of springtides is 
twice that of neaptides. 

APPENDIX K. 

Recent observations indicate that in the polar oceans, 
where evaporation is small, the cold surface water is some- 
what reduced in density by the supply of fresh water from 
rain, snow, and rivers. The polar surface water is therefore 
not quite so dense as the somewhat less cold but Salter surface 
water in latitude 60° or thereabouts. Hence the simple plan 
of the convectional movement of the underwaters between 
the poles and the equator should be modified by the addition 
of a subordinate movement that carries dense cold salt water 
from latitude 60° or thereabouts poleward underneath the still 
colder but less salt and less dense water of the polar oceans. 
It is in this way that the slight increase of temperature in 
the deep polar waters, discovered in the Antarctic by the 
Challenger expedition, and in the Arctic by Nansen, can be 
accounted for. 



APPENDIXES. 409 

APPENDIX L. 

References for Supplementary Reading. 

The titles in the following list have been selected with especial 
reference to their accessibility in public libraries. Frequent mention 
is made of the publications of the U. S. Geological Survey because 
of their great value to the geographer as well as of theu' wide distri- 
bution. 

General References. 

Gannett, The United States, Stanford's Compendium of Geography, 
Edward Stanford, 1898. 

The Annual Reports, Bulletins, Monographs, and Geological Folios 
of the U. S. Geological Survey. Many of the more geographical 
essays are referred to below. (Abbrev., G. S, Ann. Rep., etc.) 

The following geographical periodicals contain a great amount of 
material serviceable in teaching : 

National Geographic Magazine, Washington, D. C. (Abbrev., N. G. M.). 

Bulletin of the American Geographical Society, New York. 

Journal of School Geography, Lancaster, Pa. (J. S. G.). 

Geographical Journal, London. 

Scottish Geographical Magazine, Edinburgh (S. G. M.). 

Platt, The Better Books in School Geography, J. S. G., May, '98. 

(All the books mentioned in the above article would be found serviceable 
in school libraries.) 

Davis, The Equipment of a Geographical Laboratory, J. S. G., 

May, '98. 
Cornish, Laboratory Work in Elementary Physiography, J. S. G., 

June, Sept., '97. 
National Geographic Monographs, American Book Co., 1895. 
Preliminary Report of Committee on Physical Geography of N. E. 

A.; J. S. G., Sept., '98. 
Shaler, History of the Earth. D. Appleton & Co., 1898. 



410 PHYSICAL GEOGRAPHY. 



Chapter TI. — General References. 

Young, Astronomy. Ginn & Company, 1888. 
Todd, Astronomy. American Book Co., 1897. 

Chapter III. — General References. 

Waldo, Elementary Meteorology. American Book Co., 1896. 
Davis, Elementary Meteorology. Ginn & Company, 1894. 
Jameson, Elementary Meteorology, J. S. G., Jan., Feb., March, 

April, '98. 
Greely, American Weather. Dodd, Mead & Co., 1888. 
Harrington, Rainfall of the United States, U. S. Weather Bureau, 

Bulletin C, 1894. 
Greely, Rainfall Types of the United States, N. G. M., v, 45. 

Special References. 

PAGE 

53. Davis, The Temperate Zones, J. S. G., May, '97. 

53. Ward, Climatic Control of Occupation in Chile, J. S. G., 

Dec, '97. 
55. Merriam, Geogr. Distribution of Terrestrial Animals and 

Plants, N.G.M., vi, 229. 

Chapter IV. — General References. 

Thomson, The Depths of the Sea. Macmillan & Co., 1874. 
Thomson, The Voyage of the Challenger : The Atlantic. Macmillan 

& Co., 1877. 
Sigsbee, Deep Sea Sounding and Dredging, Washington, 1880. 
Agassiz, Three Cruises of the Blake, Cambridge, 1888. 
Monthly Pilot Charts of the North Atlantic and the North Pacific 

Oceans, U. S. Hydrographic Office, Washington. 

Special References. 

PAGE 

72, 83. Davis, Waves and Tides, J. S. G., April, '98. 

76. SciDMORE, Earthquake Wave, Japan, N. G. M., vii, 285. 



APPENDIXES. 411 

PAGE 

77. Davis, Winds and Ocean Currents, S. G. M., Oct., '97, and 

J. S. G., Jan., '98. 
81. PiLLSBURV, The Gulf Sti-eam, Ann. Rep. U. S. Coast Survey, 

1890. 
84. Tide Tables, published annually by U. S. Coast Survey. 

Chapter V. — General References. 

Shaler, Aspects of the Earth. Charles Scribner's Sons, 1889. 
Text-books on Elementary Geology by Dana, Geikie, Leconte, Scott, 
and Tarr. 

Special References. 

PAGE 

107. Heilprin, Distribution of Animals. D. Appleton & Co., 1886. 
107. Beddard, Zoogeography. University Press, Cambridge, 

189.5. 
107. MacMillan, Geogr. Distribution of Plants, J. S. G., 

April, '97. 

109. Wallace, Island Life. Macmillan & Co., 1891. 

110. Wallace, Travels in the Malay Archipelago. Macmillan 

& Co., 9th ed. 

Chapter VI. — Special References. 

117, 119. Davis, Description of the Harvard Geographical Models, 
published by the Boston Society of Natui'al History, 
Berkeley Street, Boston. 

123. Glenx, South Carolina, J. S. G., Jan., Feb., '98. 

125. Cobb, North Carolina, J. S. G., Nov., Dec, '97. 

126. Shaler, The Dismal Swamp, G. S. 10th Ann. Rep., 313. 

126. Chamberlin, Artesian AVells, G. S. 5th Ann. Rep., 125. 

127. McGee (Fall line), G. S. 12th Ann. Rep., 360. 
130. McGee, Chesapeake Bay, G. S. 7th Ann. Rep., 548. 
139. Ramsay, Physical Geology and Geography of Great Britain, 

London, 6th ed., 1894, 333. Edward Stanford, 1894. 
144. Powell, Exploration of the Colorado river of the west, 
Washington, 1875. See pp. 98-102, 130, 131. 



412 PHYSICAL GEOGBAPHY. 

PAGE 

144, 155. Button, Colorado Canyon, G. S. 2d Ann. Rep., 49. 

144, 155. Button, Colorado Canyon, G. S. Monogr. II. 

147. Campbell and Mendenhall (Plateau of West Virginia), 

G. S. 17th Ann. Eep., 480. 
149. EoosEVELT, Winning of the West, vol. i, 101; vol. iii, 13. 

G. P. Putnam's Sons, 1894. 
149. Semple, Influence of the Appalachian Barrier upon Colonial 

History, J. S. G., Feb., '97. 
151. Hodge, The Enchanted Mesa, N. G. M., viii, 273. 
154. Marbut, Missouri, J. S. G., April, May, '97. 



Chapter VII. — Special References. 

161. Russell, Southern Oregon, G. S. 4th Ann. Rep., 435. 

165. Russell (Mountains of Nevada), G. S. Monogr. XI, 38. 

169. Newton (edited by Gilbert), Geology of the Black Hills, 

Washington, 1880. 

172. Fay, Canadian Alps, J. S. G., June, '97. 

172. WiLLCOx, Canadian Rockies, J. S. G., Dec, '97. 

172. Lubbock, Scenery of Switzerland. Macmillan & Co., 1896. 

183. Milne, Earthquakes. D. Appleton & Co., 1883. 

186. Beddard, Zoogeography. University Press, Cambridge, 

1895. 

187. Willis, Round about Asheville, N. C, N. G. M., i, 291. 

188. McGee, Geogr. History of the Piedmont Plateau, N. G. M., 

vii, 261. 

188. Keith (Piedmont Plateau), G. S. 14th- Ann. Rep., 366. 

190. Willis, Northern Appalachians, Natl. Geogr. Monogr. 

190. Hayes, Southern Appalachians, Natl. Geogr. Monogr. 

190. Davis, Rivers and Valleys of Pennsylvania, N. G. M., i, 183. 

192. Davis, Southern New England, Natl. Geogr. Monogr. 

192. Davis, Geographical Illustrations (Southern New England), 
published by Harvard University, Cambridge, Mass. 

194. A. Geikie, Scenery of Scotland, 2d ed. (chapters on High- 
lands). Macmillan & Co., 1887. 



APPENDIXES. 413 

PAGE 

194. Herbertson, Geography of Scotland, J. S. G., May, '98. 
198. Irving (Baraboo ridge), G. S. 7th Ann. Rep., 399. 

Chapter VITI. — General References. 

Russell, Volcanoes of North America. Macmillan, 1897. 
Dana, Characteristics of Volcanoes. Dodd, Mead & Co., 1890. 
JuDD, Volcanoes. D. Appleton & Co., 1881. 
Dodge, Volcanoes, J. S. G., June, '97. 

Special References. 

PAGE 

202, 203. Lyell, Principles of Geology (Monte Nuovo, vol. i, 

p. 607 ; JoruUo, vol. i, p. 585). D. Appleton & Co., 
1872. 

203. DiLLER, A Late Volcanic Eruption in Northern California, 

G. S. Bull. 79. 

207. Phillips, Vesuvius. Macmillan & Co., 1869. 

207. Milne, Earthquakes. D. Appleton & Co., 1883. 

210. DuTTON (Lava Flows), G. S. Monogr. II. 

213. DuTTON, Hawaiian Volcanoes, G. S. 4th Ann. Rep., 81. 

214. Diller, Mt. Shasta, Natl. Geogr. Monogr. 
216. Diller, Crater Lake, N. G. M., viii, 33. 

216. Diller, Crater Lake, J. S. G., Nov., '97. 

217. DuTTON, Volcanic Necks of Zuni Plateaus, G. S. 6th Ann. 

Rep., 164. 
217. Gilbert, Geology of the Henry Mountains, Washington, 

1877. 
217. Cross, Laccolites, G. S. 14th Ann. Rep., 165. 

Chapter IX. — General References. 

Gilbert, Geology of the Henry Mountains, Washington, 1877. 

Chapter on Land Sculpture, p. 99. 
Russell, Lakes of North America. Ginn & Company, 1894. 
Brigham, Lakes, a Study for Teachers, J. S. G., March, '97. 
Russell, Rivers of North America. G. P. Putnam's Sons, 1898. 



414 PHYSICAL GEOGRAPHY. 



Special References. 

PAGE 

225. HovEY, Mammoth Cave, J. S. G., May, '97. 

226. Walcott, Natural Bridge of Virginia, N. G. M., v, 59. 
228. Weed (Hot Springs), G. S. 9th Ann. Rep., 613. 

232. Bell, Tlie Labrador Peninsula, S. G. M., xi, 335. 

232, Gilbert, Niagara, Natl. Geogr. Monogr. 

246, Gannett, Mississippi Flood of April, 1897, S. 6. M., Au- 
gust, '97. 

249. Davis, Seine, Meuse, and Moselle, N. G. M., vii, 189, 228. 

257. Lubbock, Scenery of Switzerland, 133, 312. Macmillan 
& Co., 1896. 

259. DeKalb, Valley of the Amazon, J. S. G., Sept., '97. 

Chapter X. — Special References. 

265. Shaler, Origin and Nature of Soils, G.S. 12th Ann. Rep., 219. 
276. Lubbock, Beauties of Nature. Macmillan & Co., 1892, 264. 
285. Powell, Exploration of the Colorado River of the "West, 

Washington, 1877. (Green River basin.) 
289. PuMPELLY, Researches in China, Smithsonian Contributions, 

No. 202, 1866, p. 48. 

Chapter XI. — General References. 

Russell, Glaciers of North America. Ginn & Company, 1897. 
Shaler and Davis, Glaciers. James R. Osgood & Co., 1881. 
Tyndall, Forms of Water. D. Appleton & Co., 1872. 
J. Geikie, Great Ice Age, 3d ed., D. Appleton & Co., 1895. 
Wright, Ice Age in North America. D. Appleton & Co., 1890, 

Special References. 

PAGE 

303. Gilbert, Geology of the Henry Mountains, Washington, 

1877, Chapter on Land Sculptui-e. 
306. Russell, Past and Present Lakes of Nevada, Natl, Geogr, 

Monogr, 



APPENDIXES. 415 

PAGE 

309. King, Geol. Survey of the dOth Parallel, Washington, vol. i, 
1878, 460, 484; vol. ii, 1877, 470. 

317. PuMPELLY, Researches in China, Smithsonian Contribu- 

tions, No. 202. 

318. Gilbert, Lake Bonneville, G. S. 2d Ann. Eep., 169. 

318. Gilbert, Lake Bonneville, G. S. Monogr. T. 

319. Russell, Lake Lahontan, G. S. 3d Ann. Rep., 195. 
322. McGee, Seriland, N. G.M., vii, 125. 

324. Jennings-Bramley, Journey to Siwa, Geogr. Journ. 

(London), Dec, '97. 
326. Nansen, First Crossing of Greenland, 1890. Longmans, 

Green & Co., 1890. 
32&. Peary, Northward over the Great Ice. Frederick A. Stokes 

Co., 1898. 
330. Russell, Glaciers of Alaska, G. S. 13th Ann. Rep., 7. 
330. Russell, Mt. St. Elias, Alaska, N. G.M., iii, 53. 
330. Reid, Muir Glacier, Alaska, N. G. M., iv, 19. 

330. Russell, Existing Glaciers of the U. S., G. S. 5th Ann. 

Rep., 303. 

331. Russell, Mono Lake Region, G. S. 8th Ann. Rep., pt. I, 

321. 

332. A. Geikie, Scenery of Scotland, 2d ed., chapters on Glacial 

Action. Macmillan & Co., 1887. 

333. Chamberlin, Rock Scorings, G. S. 7th Ann. Rep., 155. 

334. Chamberlin, Terminal Moraines, G. S. 3d Ann. Rep., 295. 
337. Todd, Terminal Moraines in Dakota, G. S. Bull. No. 144, 16. 
337. McGee (Drift Plains of Iowa), G. S. 11th Ann. Rep., 393. 

Gilbert, Modification of Great Lakes by Earth Movement, 
N. G. M., viii, 233. 

339. Upkam, Glacial Lake Agassiz, G. S. Monogr. XXV. 

340. Taylor, Studies in Indiana Geography, Terre Haute, 1897. 

Short History of the Great Lakes. 

344. Dryer, Studies in Indiana Geography, Terre Haute, 1897. 

The Morainic Lakes of Indiana. 

345. Bell, The Labrador Peninsula, S. G.M., xi, 335. 



416 PHYSICAL GEOGRAPHY. 



Chapter XII. — Special References. 

PAGE 

351. Shaler, Seacoast Swamps of Eastern U. S., G. S. 6th Ann. 

Rep., 359. 
351. Shaler, Sea and Land. Charles Scribner's Sons, 1894. 
354. Gilbert, Features of Lake Shores, G. S. 5th Ann. Rep., 75. 

358. Shaler, Natural History of Harbors, G. S. 13th Ann. 

Rep., 93. 

359. Hatcher (Savages and Shore Lines in Patagonia), N. G. M., 

viii, 306, 312. 
366. A. Geikie, Scenery of Scotland, 2d ed. (Shore Features). 

Macmillan & Co., 1887. 
379. Darwin, Coral Reefs. D. Appleton & Co., 1889. 
382. Dana, Corals and Coral Islands. Dodd, Mead & Co., 1890. 
382. A; Agassiz, Letter in Amer. Journ. Science, Feb., 1898. 



APPENDIX M. 

The following list of map-sheets, selected from those published by 
the U. S. Geological Survey and the U. S. Coast and Geodetic Sur- 
vey, will be found of service in illustrating various examples of land 
forms referred to in Chapters VI to XII. Complete lists of maps 
published by these Surveys can be had, free of charge, on application. 
The sheets here named might be supplemented by many others in 
illustration of special localities. Some account of the cost and of 
the method of ordering and using the maps is given in the Journal 
of School Geography, September, 1897, and October, 1898. Coast 
Survey maps are here marked " C. S." The others, unless specially 
designated, are published by the Geological Survey. 

Chapter VI. — Plains and Plateaus. 

PAGE 

113. Relief Map of New Jersey, published by the State Geological 

Survey, Trenton, N. J. ; price, 25 cents. 
130. Nomini, Md. 



APPENDIXES. 417 

PAGE 

138. Niagara Falls, Syracuse, 'Oneida, Ithaca, Elmira, N. Y. 
140-153. Topographic Atlas of the United States, folio 1, Physio- 
graphic Types, Pis. I-III. 
141. Mt. Trumbull, Diamond Creek, Ariz. 
147. Kanawha Falls, Nicholas, W. Va. 

150. Sewanee, Tenn. ; Kaaterskill, N. Y. 

151. Watrous, Corazon, N. M. ; Abilene, Brownwood, Tex. 
Springfield, Bolivar, Tuscumbia, Mo. 

Mt. Trumbull, Kaibab, Echo Cliffs, Ariz. 

Chapter VII. — Mountains. 

165. Disaster, Nev. ; Alturas, Cal. 

170. Deadwood, Rapid City, S. D. 

172. Platte Canyon, Huerfano Park, Col. 

187. Asheville, Mt. Mitchell, Pisgah, N. C. 

190. Atlanta, Ga. (Stone mountain is a fine example of a monad- 
nock on the uplands of Georgia.) 

190. Harrisburg, Hummelstown, Lykens, Pa. 

192. Chesterfield, Granville, Mass. ; Winsted, Derby, Bridgeport, 
Conn. 

196. C. S. No. 710. 

Chapter VIII. — Volcanoes. 

215. Shasta, Cal.; San Francisco Mountain, Ariz. 

216. Crater Lake (special sheet), Oregon. 

Chapter IX. — Rivers and Valleys. 

226. Citra, Fla. 

229. Gallatin, Shoshone, Yellowstone National Park. 

239. Mesa de Maya, Col. 

242. Versailles, Tuscumbia, Mo. 

243. Minden, Nebr. 

245. 8-Sheet Map of the Alluvial Valley of the Mississippi River, 
published by the Mississippi River Commission, St. Louis, Mo. 



418 PHYSICAL GEOGRAPHY. 

PAGE 

249. Dahlonega, Gainesville, Walhalla, Ga. 

252. Great Falls, Mont. 

255. Delaware Watergap, Pa.; Harpers Ferry, Va. 

260. New London, Norwich, Conn.; State Map of Rhode Island. 

261. Haarlem, Tarrytown, West Point, Poughkeepsie, N. Y. 

Chapter X. — The Waste of the Land. 

277. Lake, Wyo. (Two-Ocean Creek). 

279. Independence, Marshall, Mo. 

286, Donaldsonville, La. 

287. 8-Sheet Map of the Alluvial Valley of the Mississippi Eiver. 

(See above.) 

293. C. S. No. 194. 

Chapter XI. — Climatic Control of Land Forms. 

306. Disaster, Granite Range, Long Valley, Nev. 

334. Springfield, Mass.; Cohoes, N. Y. 

334. Topographic Atlas of the United States, folio 1, PL VI. 

338. Oconomowoc, Sun Prairie, Wis. 

342. Elizabethtown, Mt. Marcy, N. Y. 

343. Oriskany, N. Y.; Minneapolis, St. Paul, Minn.; Marseilles, 

Ottawa, Lasalle, 111. 

343. Rochester, N. Y.; Minneapolis, Minn. 

Chapter XII. — Shore Lines. 

351. C. S. No. 21. 

351. C. S.Nos. 30, 204. 

352. C. S. Nos. 11, 14.5, 419. 

352. C. S. Nos. 123, 154. 

353. C. S. No. 143. 

354. Asbury Park, Sandy Hook, N. J., C. S. No. 121. 
357. C. S. No. 408. 

364. Martha's Vineyard, Gay Head, Mass., C. S. No. 112. 

371. C. S. No. 194. 



IJSTDEX. 



Adirondacks, 138, 342. 
Agriculture, 36, 282, 124, 125. 

and irrigation, 45, 288. 

and soil, 7, 124, 134, 189, 268. 

Alabama, 134, 146. 
Alaska, 195, 196, 327, 330. 
Allegheny mountains, 190, 256. 

plateau, 138, 146, 149, 194, 

200, 242. 

river, 254. 

Alluvial fans, see Fans. 

Alps, 172, 177, 184, 186, 256, 277. 

glaciers of, 327, 329, 330, 332. 

Amazon, 237, 259. 

Andes, 31, 177, 302, 306, 330. 

Andorra, 185. 

Animals, in caves, 225. 

and climate, 55. 

on deserts, 321. 

distribution, l07. 

on islands, 109, 381. 

on mountains, 175, 186. 

in ocean, 88, 106. 

Antarctic regions, 66, 325. 
Anticyclones, 34, 49, 405. 
Ants, 267, 310. 
Arabia, 316. 
Argentina, 177, 301. 
Argon, 25. 
Aristotle, 11. 



Arizona, climate, 298, 312. 

• plateaus, 144, 151, 155, 324. 

volcanoes, 214, 218. 

waste slopes, 309. 

Arkansas river, 282. 
Artesian wells, 126, 137, 228. 
Atlantic City, 115, 127, 353. 
Atlantic ocean, 40, 62, 66, 69, 78, 

81, 82. 
Atmosphere, 22, 23, 25, 27, 29, 402. 
Atolls, 379, see Reefs. 
Australia, 109, 376. 
Avalanches, 178. 
Azores, 212. 

Bad lands, 303. 
Baltimore, 131. 
Banks, 352. 
Baraboo, 198. 
Barometer, 23. 
Baselevel, 120. 
Basin, interior, 304, 307. 

river, 230. 

rock, 342, 345, see Lakes. 

waste-filled, 281, 284, 307, 311, 

317, see Waste. 
Basques, 185. 
Bays, 129, 131, 196, 296, 357, 358, 

365. 
Beach, 351, 362, 363, 364. 



419 



420- 



PHYSICAL GEOGRAPHY. 



Beavers, 107. 
Bedouins, 18. 
Bench, 360. 
Black Hills, 169. 
Black Rock desert, 306. 
Blue Ridge, 187, 256. 
Bluff, 353, 354, see Cliff. 
Bolivia, 306. 
Bore, 87. 

Boulder clay, 336. 
Boundaries, 17, 177, 249. 
Brazil, 31. 

Bristol channel, 365. 
British Columbia, 196, 295. 
British Guiana, 152. 
Buenos Ayres, 231, 233, 350. 
Butte, 150, 216, 217, 221. 

Caldera, 212, 213, 215. 
California, climate, 21, 37, 302. 

coast, 118. 

• fans, 288, 308. 

moraines, 331. 

mountains, 167, 195. 

valley, 288, 291. 

volcanoes, 203, 214, 220. 

Calms, 32. 

Camel, 18, 321. 

Canada, 137, 217, 232, 333, 344, 

345. 
Canals, 232, 341. 
Canyons, 141, 144, 148, 156, 158, 

218. 
Carbonic acid, 25, 26. 
Caribou, 108. 
Cassowary, 109. 
Catskill moimtains, 146. 
Caucasus, 175, 185, 330. 
Caverns, 225, 362. 
Central America, 31, 206, 208. 



Chagos bank, 378. 

Charleston, 125, 353. 

Chattahoochee, 249. 

Chesapeake bay, 130, 228, 260. 

Chicago, 341. 

Chili, 37, 177, 299. 

China, 177, 289, 294, 317. 

Chinook wind, 176. 

Chippewa, 334. 

Chunnenugga ridge, 135. 

Cinder cone, 204. 

Cliff dwellers, 146. 

Cliffs, 143, 147, 156, 158, 196, 269. 

sea, 219, 355, 360, 363, 366. 

Climate, 20, 52, 153, 297. 

and animals, 55, 321. 

and land forms, 297. 

and man, 56. 

and plants, 54, 319. 

and shore lines, 372, 374. 

changes of, 298, 318. 

dry, 46, 299, 319. 

glacial, 324. 

of lands, 98. 

of mountains, 167, 175, 176. 

of plains, 140, 153. 

• of plateaus, 144, 153. 

Cloudbursts, 145, 300. 
Clouds, 403, 404. 
Coal, 149. 
Coastal plains, 118, 122. 

ancient, 136, 137, 139. 

belted, 132, 247, 249. 

embayed, 129. 

Cold wave, 21, 49. 
Colorado, 208, 272, 316, 331. 
Colorado canyon and river, 144, 

156, 189, 235, 301. 
Columbia, 125. 
Columbus, 398. 



INDEX. 



421 



Commerce, 7, 20. 

Congo, 237. 

Conical projection, 395. 

Connecticut, 192, 334. 

Conseguina, 206. 

Continental shelf, 70, 96, 104. 

Continents, 93, 94, 95. 

Contours, 397. 

Coral reefs, see Eeefs. 

Cotopaxi, 207. 

Cotton, 20, 125, 135. 

Crater, 202. 

Cuba, 375, 377. 

Cuesta, 133. 

Cumberland plateau, 146. 

Currents, 77, 79, 81, 97, 364, 375, 

Cyclones, 34, 39, 49, 405.' 

Dacia bank, 208. 

Dakota, North and South, 169. 

303, 335, 337, 
Danube, 285, 292. 
Dead sea, 305, 307. 
Deception island, 213. 
Dekkan, 122. 
Delaware bay and river, 130, 255, 

296. 
Deltas, 130, 196, 197, 292, 294, 369, 

370. 

dissected, 296. 

in lakes, 234. 

tidal, 353. 

Denudation, 105. 

Denver, 300. 

Deserts, 18, 30,46, 146, 301, 306, 333. 

Dew, 47. 

Dikes, 216, 221. 

Distributaries, 293. 

Divides, 230, 246, 250, 251, 312, 

344. 



Doldrums, 32, 37, 39, 81, 97. 
Dredge, 62. 
Drift, glacial, 328. 
Drought, 21, 320. 
Drumlins, 338. 

Dunes, 104, 315, 351, 353, 354. 
Dust, 314, 316, 317, 
Dwarfs, 2, 5, 19, 

Earth, 8, 9, 15, 19, 400. 

shape and size, 10, 12, 13, 14, 

385, 386. 
Earthquakes, 76, 163, 166, 183, 

187, 199, 207. 

waves, 75, 76. 

Ecuador, 207. 
Enchanted mesa, 151. 
England, 139, 365. 
Equinox, 401. 
Eratosthenes, 386. 
Erosion, 105, 181. 

glacial, 329. 

Eruptions, 199, 201, 205. 
Erzgebirge, 195. 
Escarpments, 156. 
Eskers, 337. 
Eskimos, 4, 19, 326. 
Eudoxus, 385. 

Fall line, 127, 134. 

Falls, 127, 134, 144, 234, 236, 252, 

338, 342. 
Famines, 21. 

Fans, 162, 166, 275, 288, 295, 307. 
Faroe, 219. 
Faults, 158, 162, 165. 
Feldspar, 101. 
Fertilizers, 125. 
Fiji, 378, 382. 
Fingal's cave, 362. 



422 



PHYSICAL GEOGRAPHY. 



Finland, 345. 

Fiords, 196, 345, 358, 369. 

Fisheries, 44, 71, 131, 134. 

Flood plain, 242, 244, 279, 280, 

286, 301, 333. 
Floods, 21, 148, 206, 211, 246, 277, 

289, 310, 313. 

and lakes, 182, 234. 

sea, 294, 350. 

Florida, 21. 

Foehn wind, 176. 

Forests, 2, 32, 125, 135, 148, 208, 

218, 273. 
on mountains, 171, 174, 176, 

188, 193. 
Fossils, 71, 96, 102, 119, 136, 173. 
France, 177, 215, 220, 249, 253. 
Fraser river, 253, 295. 
Frost, 47. 
Fundy, Bay of, 87, 365. 

Galapagos, 375. 

Galveston, 351. 

Ganges, 293, 294. 

Genoa, 118. 

Georgia, 249. 

Germany, 188, 191, 195, 254, 287. 

Geysers, 229. 

Giants' causeway, 219. 

Gibraltar, 366. 

Glacial period, 330. 

Glacier, 325, 328, 330. 

Alpine, 326. 

ancient, 331. 

Laurentian, 333. 

Scandinavian, 333. 

Glens, 194. 
Globes, 393. 
Globigerina, 68, 103. 
Gold, 195, 220. 



Gorges, 183, 282, 342, 348. 

Grand wash, 156. 

Granite, 101, 193, 225. 

Gravity, 15. 

Grazing, 37, 140, 153, 170, 176, 

186, 221, 320. 
Great Basin, 304, 306. 
Great Lakes, 340, 341, 355. 
Greece, 295. 

Greek philosophers, 11, 12. 
Green river basin, 285. 
Greenland, 4, 326. 
Ground water, 224, 227, 278, 292. 
Gulf Stream, 81. 

Hachures, 396. 

Hail, 45. 

Harbors, 196, 354, 356, 358, 375. 

Harvard geographical models, 394. 

Hatteras, 352. 

Hawaiian islands, 213. 

Headlands, 358, 364, 365. 

Herculaneum, 207. 

Highlands of Scotland, 194, 196, 

332, 366. 
Himalaya, 172, 177, 181, 258, 280, 

284, 312, 327. 
Hoangho, 289, 293, 294. 
Hood, Mount, 214. 
Horse, 140. 
Horse latitudes, 33. 
Hudson river, 261. 
Hungary, 244, 285. 
Hurricane ledge, 156. 
Hurricanes, 22, 39, 75, 294. 

Ibex, 186. 
Ice, 65, 234. 

falls, 179. 

sheets, 325, 333. 



INDEX. 



423 



Icebergs, 66, 325, 326. 

Iceland, 210, 229. 

Idaho, 211, 218. 

Illinois, 334, 344. 

India, 46, 122, 177, 219, 258, 290, 

294, 308. 
Indian ocean, 43, 80. 
Indiana, 334, 344. 
Indians, 145, 304, 322. 
Inlets, 352. 
Iowa, 338. 
Iron ore, 149, 195. 
Irrigation, 37, 45, 288, 308. 
Islands, 67, 71, 196, 358, 360, 365, 

369, 372. 

coral, 67, 379. 

volcanic, 67, 203, 209. 

Isotherms, 29, 34, 35. 
Italy, 202, 207, 294. 

Jaguar, 108. 
Japan, 76, 207, 294. 
Java, 207. 
JoruUo, 203. 
Jura, 167. 

Kaibab plateau, 157, 158. 
Kanauha river, 258. 
Kangaroo, 110. 
Kansas, 21. 
Kashmir, 284. 
Kentucky, 147, 268. 
Klondike, 195. 
Krakatoa, 24, 76. 
Krypton, 25. 

Lagoons, 351, 353, 370. 
Lake Agassiz, 339. 

Bonneville, 318. 

Crater, 215, 216. 



Lake Erie, 138, 281, 354. 

Geneva, 234, 295. 

Great Salt, 305, 307, 318. 

Itasca, 344. 

Lahontan, 319. 

Nyassa, 233. 

Pepin, 334. 

Shirwa, 305. 

Snag, 204. 

Titicaca, 306. 

Van, 305. 

Victoria Nyanza, 233. 

Lakes, 226, 232, 245, 256, 276, 282, 

291, 302. 

Alpine, 256. 

glacial, 335, 339, 341, 345. 

in mountains, 163. 

salt, 305, 311. 

shore lines, 354, 360. 

temperature, 233, 234. 

volcanic, 211, 213, 214. 

Land and sea breezes, 44. 
Lands, 91, 93, 95, 98, 104, 105. 

waste of, 70, 101, 103. 

Landslides, 162, 181, 184, 187, 270, 

280. 
Latitude, 17, 388, 391. 
Lava, 103, 200, 201. 
flows, 204, 209, 210, 219, 

268. 

plateaus, 211, 218. 

table mountains, 219. 

Ledges, 298. 
Life, 88, 105, 109. 
Limestone, 102, 225, 226, 266. 
Llanos, 320. 
Loess, 317. 
Long Branch, 354. 
Longitude, 17, 388, 391. 
Lookout, Cape, 352. 



424 



PHYSICAL GEOGRAPHY. 



Madras, 122. 

Magnetic poles, 399. 

Magnetism, terrestrial, 398. 

Maine, 372. 

Mammoth cave, 225. 

Man, races of. 111. 

Manchester, 237. 

Mangrove, 373. 

Maps, 393. 

Marquesas islands, 379. 

Marsh, 140, 305, 311, 351. 

Massachusetts, 192, 339. 

Meander belt, 245. 

Meanders, 241, 243, 253, 284. 

Mercator projection, 395. 

Merced river, 288, 291. 

Meridians, 16, 17, 391. 

Merrimac, 334, 343. 

Merc, 324. 

Mesa, 150, 219, 221. 

Meuse river, 249. 

Mexico, 31, 121, 203, 208, 299, 312, 

357. 
Mica, 101. 
Michigan, 149. 

Mining, 134, 137, 149, 171, 195. 
Minneapolis, 237, 343. 
Minnesota, 149, 337. 
Mississippi river, 237, 239, 259, 

338, 340, 344. 

• delta, 293, 296, 369. 

flood plain, 21, 244, 246, 286, 

287. 

meanders, 245. 

Missouri, 154, 242, 252, 338. 

river, 220, 242, 279. 

Models, 393, 394. 
Mohawk, 138, 223, 341. 
Monadnock, 190, 193, 197. 
Monsoons, 40, 43, 88. 



Montana, 220. 
Monte Nuovo, 202. 
Moon, 86, 406. 
Mountains, 159, 164, 176. 

buried, 218. 

embayed, 195, 295. 

lofty, 172, 174, 204, 292, 293, 

330. 

old, 167, 188, 372. 

subdued, 187. 

young, 161, 163, 167. 

Moraines, 328, 334, 335. 
Moselle river, 249, 254. 
Mt. Blanc, 174. 

Nansen, 79, 326. 

Narragansett bay, 260. 

Natural bridges, 226. 

Navigation, 39, 60, 67, 78, 81, 87, 

353, 358. 

river, 128, 236, 237, 260. 

Nebraska, 21. 

Neckar river, 254. 

Necks, volcanic, 216. 

Netherlands, 97, 354. 

Nevada, 161, 164, 309, 319. 

New England, 20, 192, 336. 

New Hampshire, 192. 

New Jersey, 113, 255, 296, 352, 

354, 357. 

New Mexico, 151, 214, 218, 316. 
New York, 146, 262, 339. 
Newton, 12, 86. 
Niagara, 137, 232, 234, 341, 

343. 
Nile, 38, 233, 301, 387. 
Nitrogen, 25. 
Nomads, 140, 153. 
Norfolk, 131. 
Normandy, 253, 356, 359. 



INDEX. 



425 



North Carolina, 125, 187, 342, 351, 

357. 
Norway, 345, 358, 368. 

Oasis, 322, 323. 

Oceans, 57, 59, 61, 67, 69, 77, 88, 

104. 
Ohio, 147, 334, 337. 

river, 234, 243, 344. 

Ontario, 137. 

Ooze, 68. 

Oregon, 161, 211, 214, 215, 218. 

Osage river, 242. 

OxbovF lake, 245. 

Oxygen, 25, 26, 64. 

Ozark plateau, 154. 

Pacific ocean, 40, 43, 53, 67, 76, 

375, 378. 
Parallels, 16, 17, 388. 
Pamlico sound, 130. 
Pass, 177. 
Patagonia, 359. 

Peaks, 174, 180, 271, 272, 273. 
Peary, 326. 
Peedee river, 370. 
Peneplain, 152. 
Pennsylvania, 137, 190, 242, 255, 

296. 
Persia, 308, 311. 
Peru, 302, 320. 

Piedmont belt, 188, 190, 253, 274. 
Pikes peak, 272. 
Plains, 1.39, 152, 221. 
coastal, 118, 122, 349, 355, 

372. 

dust, 316. 

glacial, 337. 

river-made, 290, 291, 292. 

Planets, 9. 



Plants, 15, 54, 90, 105, 107, 224, 

319. 

on atolls, 380. 

on deserts, 319. 

on mountains, 175. 

on plateaus, 146. 

Plateaus, 141, 145, 150, 155, 271. 

Platforms, 143. 

Platte river, 243. 

Playas, 306. 

Po, 292. 

Population, 118, 322. 

of mountains, 184, 188, 194. 

of river-made plains, 289, 292, 

294. 

See Settlements. 
Potomac river, 256, 260, 262, 296. 
Prairies, 135. 
Projection of maps, 394. 
Promontories, 196, 358, 372. 
Pyrenees, 177, 185. 

Quartz, 101, 275. 

Races of men. 111. 
Railroads, 134, 178, 193, 254. 
Rain gauge, 45. 
Rainfall, 1, 31, 37, 45, 403. 

and agriculture, 45, 156, 320. 

on mountains, 164, 171, 175, 

299. 
Rapids, 144, 234, 254, 338, 342, 

345. 
Red river, 280. 
Reefs, coral, 374, 377, 382. 

sand, 121, 129, 350, 353, 370. 

Relief, 396. 

Rhine, 192, 252, 259, 287, 292. 

Rhone, 234. 

Ridges, 174, 180. 



426 



PHYSICAL GEOGRAPHY. 



Rio Grande, 371. 

Rivers, 222, 230, 238, 243, 299, 356. 

antecedent, 258.. 

dismembered, 260. 

engrafted, 259. 

graded, 237. 

mature, 250. 

old, 251. 

revived, 252. 

w^ithering, 300, 304. 

young, 163, 231, 329. 

Roads, 149, 224. 

in mountains, 177, 186, 193, 

285. 

on plains, 115, 121, 134. 

Rochester, 237, 343. 

Rock basins, 342, 345. 

Rock waste, see Waste. 

Rocks, 101. 

Rocky mountains, 172, 175, 253, 

270, 330, 331. 
Roraima, 152. 
Rotation of earth, 15. 
Russia, 152, 153, 185. 

Sahara, 18, 30, 299, 315, 320, 323, 

333. 
Salerno, 367. 
Salinas, 306. 
Salt, 63, 305, -307. 
San Luis valley, 316. 
Sand, 315, 316. 
Sand reefs, see Reefs. 
Sandstone, 101, 193. ' 
Savannah, 249, 353. 
Scale, 397. 

Scandinavia, 333, 345, 359. 
Schwarzwald, 188. 
Scotland, 194, 196, 332, 339, 366. 
Seasons, 35* 401. 



Seine, 87, 250, 253, 254, 365. 
Selkirk mountains, 175. 
Settlements on coasts, 134, 350, 
358, 367, 368. 

on mountains, 164, 167, 169, 

171, 183, 186, 193, 196. 

on plains, 114, 121, 125, 128, 

131, 134. 

on plateaus, 146. 

on rivers, 125, 134, 237, 286. 

See Population. 
Shasta, Mt., 214, 282. 
Sheavwits plateau, 144, 155, 210. 
Sheetflood, 313. 
Ships, 20, 58, 73. 
Shore lines, 347, 349, 357, 366, 372. 

of deltas, 369. 

of lakes, 360, 368. 

Siberia, 139, 233. 

Sierra Nevada, 195, 331. 

Simum, 316. 

Sinkholes, 225, 226. 

Slate mountains, 191, 259. 

Snake river, 218. 

Snow, 2, 45, 47, 177, 206, 209, 

404. 
Snow line, 176. 
Soil, 265, 268, 274, 337, 345. 
Solar system, 9. 
Solstice, 401. 
Sounding, 61. 
Sounds, 196, 357. 
South Carolina, 123, 249, 352. 
Spain, 177. 
Spits, 364. 

Springs, 163, 226, 228, 292. , 
St. Elias, Mt., 330. 
St. Helena, 75, 209. 
St. Lawrence, 232, 234, 260, 340, 

344. 



INDEX. 



A21 



Stacks, 360, 364. 
Stars, 8, 388, 400. 
Steppes, 320. 

Stereographic projection, 394. 
Storms, 21, 22, 33, 36. 
Subequatorial belts, 37. 
Subtropical belts, 37. 
Sudan, 38. 
Sun, 8, 400. 
Surf, 74. 

Susquehanna, 242, 256, 296. 
Svanetians, 185. 
Swamps, 126. 
Sweden, 345. 
Switzerland, 167, 185. 
See Alps. 

Table mountains, 219. 
Talus, 143, 146, 162, 269, 271. 
Tarim river, 311. 

Temperature of atmosphere, 27, 28, 
41. 

and currents, 81, 82. 

earth, 99. 

lakes, 233. 

oceans, 63, 69. 

Tennessee, 268. 

Terraces, 280, 334. 

Texas, 351, 352, .371. 

Thermometer, 27, 61. 

Thunderstorms, 32, 39, 45. 

Tibet, 24, 208, 311. 

Tidal deltas, 353. 

Tides, 37, 83, 87, 294, 352, 365. 

cause of, 86, 406. 

in lakes, 88. 

Tiger, 109. 
Till, .336. 

Tonga islands, 203. 
Tornadoes, 34. 



Torrents, 275, 278. 
Trade winds, 31. 
Tree line, 176. 
Tributaries, 286. 
Tropical calms, 33, 36. 
Tuamotu, 381, 382. 
Turkestan, 311. 

Uinkaret plateau, 155, 157, 210. 
Uinta mountains, 285. 
Utah, 164, 309, 318. 

Valleys, 103, 153, 222, 239, 244. 

crosswise, 169, 183, 255. 

filled, 278, 282. 

in mountains, 174, 180. 

in plains, 119, 125, 133, 153. 

in plateaus, 141, 148. 

lengthwise, 169, 183, 255. 

terraced, 278, 280. 

Vegetation, 25, 45, 54, 140. 
Venezuela, 37, 320. 
Vera Cruz, 121. 
Vermont, 192. 
Vesuvius, 200, 207, 213. 
Virginia, 1-30, 188, 357. 
Volcanoes, 12, 99, 103, 199, 201, 
205, 208, 213. 

Wadies, 299. 
Wales, 188. 
Wallace's line, 110. 
Washington, 211, 218, 268. 
Waste of the land, 143, 263, 267, 

271, 273, 275. 

and climate, 298. 

glacial, 328. 

in basins, 281, 284, 306, 309, 

311, 316. 
in valleys, 278, 282, 286, 302. 



428 



PHYSICAL GEOGRAPHY. 



Water vapor, 25, 403. 
Waterfalls, see Falls. 
Watergap, 170, 255. 
Watershed, see Divide. 
Waves, 70, 73, 104, 294, 360, 370. 

earthquake, 75. 

Weather, 21, 33, 48, 405. 

maps, 49, 405. 

■ prediction, 21, 52. 

Weathering, 13, 99, 100, 265, 267, 

271. 
Wells, 227. 
West Virginia, 147, 258. 



Westerly winds, 31, 33. 
Winds, 29, 36, 40, 44, 104, 402, 
405. 

and currents, 79. 

and denudation, 314. 

Wisconsin, 130, 197, 228, 274, 339. 
Wyoming, 285, 303. 

Yazoo river, 287. 
Yellowstone park, 26, 229, 277. 
Yellowstone river, 235. 

Zones, 27, 48, 52, 401. 



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